Royal Dutch Shell
Royal Dutch Shell plc known as Shell, is a British-Dutch oil and gas company headquartered in the Netherlands and incorporated in the United Kingdom. It is one of the six oil and gas "supermajors" and the fifth-largest company in the world measured by 2018 revenues. Shell was first in the 2013 Fortune Global 500 list of the world's largest companies. Shell is vertically integrated and is active in every area of the oil and gas industry, including exploration and production, transport and marketing, power generation and trading, it has renewable energy activities, including in biofuels, energy-kite systems, hydrogen. Shell has operations in over 70 countries, produces around 3.7 million barrels of oil equivalent per day and has 44,000 service stations worldwide. As of 31 December 2014, Shell had total proved reserves of 13.7 billion barrels of oil equivalent. Shell Oil Company, its principal subsidiary in the United States, is one of its largest businesses. Shell holds 50% of Raízen, a joint venture with Cosan, the third-largest Brazil-based energy company by revenues and a major producer of ethanol.
Shell was formed in 1907 through the amalgamation of the Royal Dutch Petroleum Company of the Netherlands and the "Shell" Transport and Trading Company of the United Kingdom. Until its unification in 2005 the firm operated as a dual-listed company, whereby the British and Dutch companies maintained their legal existence but operated as a single-unit partnership for business purposes. Shell first entered the chemicals industry in 1929. In 1970 Shell acquired the mining company Billiton, which it subsequently sold in 1994 and now forms part of BHP Billiton. In recent decades gas exploration and production has become an important part of Shell's business. Shell acquired BG Group in 2016. Shell is a constituent of the FTSE 100 Index, it had a market capitalisation of £185 billion at the close of trading on 30 December 2016, by far the largest of any company listed on the London Stock Exchange and among the highest of any company in the world. It has secondary listings on the New York Stock Exchange.
As of January 2013, Shell's largest shareholder was Capital Research Global Investors with 9.85% ahead of BlackRock in second with 6.89%. The Royal Dutch Shell Group was created in April 1907 through the amalgamation of two rival companies: the Royal Dutch Petroleum Company of the Netherlands and the Shell Transport and Trading Company Limited of the United Kingdom, it was a move driven by the need to compete globally with Standard Oil. The Royal Dutch Petroleum Company was a Dutch company founded in 1890 to develop an oilfield in Pangkalan Brandan, North Sumatra, led by August Kessler, Hugo Loudon, Henri Deterding; the "Shell" Transport and Trading Company was a British company, founded in 1897 by Marcus Samuel, 1st Viscount Bearsted, his brother Samuel Samuel. Their father had owned an antique company in Houndsditch, which expanded in 1833 to import and sell seashells, after which the company "Shell" took its name. For various reasons, the new firm operated as a dual-listed company, whereby the merging companies maintained their legal existence, but operated as a single-unit partnership for business purposes.
The terms of the merger gave 60 percent ownership of the new group to the Dutch arm and 40 percent to the British. National patriotic sensibilities would not permit a full-scale merger or takeover of either of the two companies; the Dutch company, Koninklijke Nederlandsche Petroleum Maatschappij at The Hague, was in charge of production and manufacture. The British Anglo-Saxon Petroleum Company was based in London, to direct the transport and storage of the products. During the First World War, Shell was the main supplier of fuel to the British Expeditionary Force, it was the sole supplier of aviation fuel and supplied 80 percent of the British Army's TNT. It volunteered all of its shipping to the British Admiralty; the German invasion of Romania in 1916 saw. In 1919, Shell took control of the Mexican Eagle Petroleum Company and in 1921 formed Shell-Mex Limited which marketed products under the "Shell" and "Eagle" brands in the United Kingdom. In 1929, Shell Chemicals was founded. By the end of the 1920s, Shell was the world's leading oil company, producing 11 percent of the world's crude oil supply and owning 10 percent of its tanker tonnage.
Shell Mex House was completed in 1931, was the head office for Shell's marketing activity worldwide. In 1932 in response to the difficult economic conditions of the times, Shell-Mex merged its UK marketing operations with those of British Petroleum to create Shell-Mex and BP, a company that traded until the brands separated in 1975. Royal Dutch Company ranked 79th among United States corporations in the value of World War II military production contracts; the 1930s saw. After the invasion of the Netherlands by Germany in 1940, the head office of the Dutch companies was moved to Curacao. In 1945 Shell's Danish headquarters in Copenhagen, at the time being used by the Gestapo, was bombed by Royal Air Force Mosquitoes in Operation Carthage. Around 1952, Shell was the first company to use a computer in the Netherlands; the computer, a Ferranti Mark 1*, was assembled and used at the Shell laboratory in Amste
The mollusc shell is a calcareous exoskeleton which encloses and protects the soft parts of an animal in the phylum Mollusca, which includes snails, tusk shells, several other classes. Not all shelled; the ancestral mollusc is thought to have had a shell, but this has subsequently been lost or reduced on some families, such as the squid and some smaller groups such as the caudofoveata and solenogastres, the derived Xenoturbella. Today, over 100,000 living species bear a shell. Malacology, the scientific study of molluscs as living organisms, has a branch devoted to the study of shells, this is called conchology—although these terms used to be, to a minor extent still are, used interchangeably by scientists. Within some species of molluscs, there is a wide degree of variation in the exact shape, pattern and color of the shell. A mollusc shell is formed and maintained by a part of the anatomy called the mantle. Any injuries to or abnormal conditions of the mantle are reflected in the shape and form and color of the shell.
When the animal encounters harsh conditions that limit its food supply, or otherwise cause it to become dormant for a while, the mantle ceases to produce the shell substance. When conditions improve again and the mantle resumes its task, a "growth line" is produced; the mantle edge secretes a shell. The organic constituent is made up of polysaccharides and glycoproteins; this organic framework controls the formation of calcium carbonate crystals, dictates when and where crystals start and stop growing, how fast they expand. The shell formation requires certain biological machinery; the shell is deposited within a small compartment, the extrapallial space, sealed from the environment by the periostracum, a leathery outer layer around the rim of the shell, where growth occurs. This caps off the extrapallial space, bounded on its other surfaces by the existing shell and the mantle; the periostracum acts as a framework from which the outer layer of carbonate can be suspended, but in sealing the compartment, allows the accumulation of ions in concentrations sufficient for crystallization to occur.
The accumulation of ions is driven by ion pumps packed within the calcifying epithelium. Calcium ions are obtained from the organism's environment through the gills and epithelium, transported by the haemolymph to the calcifying epithelium, stored as granules within or in-between cells ready to be dissolved and pumped into the extrapallial space when they are required; the organic matrix forms the scaffold that directs crystallization, the deposition and rate of crystals is controlled by hormones produced by the mollusc. Because the extrapallial space is supersaturated, the matrix could be thought of as impeding, rather than encouraging, carbonate deposition. Nucleation is endoepithelial in Neopilina and Nautilus, but exoepithelial in the bivalves and gastropods; the formation of the shell involves a number of genes and transcription factors. On the whole, the transcription factors and signalling genes are conserved, but the proteins in the secretome are derived and evolving. Engrailed serves to demark the edge of the shell field.
In gastropod embryos, Hox1 is expressed. Perlucin increases the rate at which calcium carbonate precipitates to form a shell when in saturated seawater. Perlucin operates in association with Perlustrin, a smaller relative of lustrin A, a protein responsible for the elasticity of organic layers that makes nacre so resistant to cracking. Lustrin A bears remarkable structural similarity to the proteins involved in mineralization in diatoms – though diatoms use silica, not calcite, to form their tests! The shell-secreting area is differentiated early in embryonic development. An area of the ectoderm thickens invaginates to become a "shell gland"; the shape of this gland is tied to the form of the adult shell. The gland subsequently evaginates in molluscs. Whilst invaginated, a periostracum - which will form a scaffold for the developing shell - is formed around the opening of the invagination, allowing the deposition of the shell when the gland
Secure Shell is a cryptographic network protocol for operating network services securely over an unsecured network. Typical applications include remote command-line login and remote command execution, but any network service can be secured with SSH. SSH provides a secure channel over an unsecured network in a client–server architecture, connecting an SSH client application with an SSH server; the protocol specification distinguishes between two major versions, referred to as SSH-1 and SSH-2. The standard TCP port for SSH is 22. SSH is used to access Unix-like operating systems, but it can be used on Microsoft Windows. Windows 10 uses OpenSSH as its default SSH client. SSH was designed as a replacement for Telnet and for unsecured remote shell protocols such as the Berkeley rlogin and rexec protocols; those protocols send information, notably passwords, in plaintext, rendering them susceptible to interception and disclosure using packet analysis. The encryption used by SSH is intended to provide confidentiality and integrity of data over an unsecured network, such as the Internet, although files leaked by Edward Snowden indicate that the National Security Agency can sometimes decrypt SSH, allowing them to read the contents of SSH sessions.
SSH uses public-key cryptography to authenticate the remote computer and allow it to authenticate the user, if necessary. There are several ways to use SSH. Another is to use a manually generated public-private key pair to perform the authentication, allowing users or programs to log in without having to specify a password. In this scenario, anyone can produce a matching pair of different keys; the public key is placed on all computers that must allow access to the owner of the matching private key. While authentication is based on the private key, the key itself is never transferred through the network during authentication. SSH only verifies whether the same person offering the public key owns the matching private key. In all versions of SSH it is important to verify unknown public keys, i.e. associate the public keys with identities, before accepting them as valid. Accepting an attacker's public key without validation will authorize an unauthorized attacker as a valid user. On Unix-like systems, the list of authorized public keys is stored in the home directory of the user, allowed to log in remotely, in the file ~/.ssh/authorized_keys.
This file is respected by SSH only if it is not writable by anything apart from the root. When the public key is present on the remote end and the matching private key is present on the local end, typing in the password is no longer required. However, for additional security the private key itself can be locked with a passphrase; the private key can be looked for in standard places, its full path can be specified as a command line setting. The ssh-keygen utility produces the private keys, always in pairs. SSH supports password-based authentication, encrypted by automatically generated keys. In this case, the attacker could imitate the legitimate server side, ask for the password, obtain it. However, this is possible only if the two sides have never authenticated before, as SSH remembers the key that the server side used; the SSH client raises a warning before accepting the key of a new unknown server. Password authentication can be disabled. SSH is used to log into a remote machine and execute commands, but it supports tunneling, forwarding TCP ports and X11 connections.
SSH uses the client-server model. The standard TCP port 22 has been assigned for contacting SSH servers. An SSH client program is used for establishing connections to an SSH daemon accepting remote connections. Both are present on most modern operating systems, including macOS, most distributions of Linux, OpenBSD, FreeBSD, NetBSD, Solaris and OpenVMS. Notably, versions of Windows prior to 1709 do not include SSH by default. Proprietary and open source versions of various levels of complexity and completeness exist. File managers for UNIX-like systems can use the FISH protocol to provide a split-pane GUI with drag-and-drop; the open source Windows program WinSCP provides similar file management capability using PuTTY as a back-end. Both WinSCP and PuTTY are available packaged to run directly off a USB drive, without requiring installation on the client machine. Setting up an SSH server in Windows involves enabling a feature in Settings app. In Windows 10 version 1709, an official Win32 port of OpenSSH is available.
SSH is important in cloud computing to solve connectivity problems, avoiding the security issues of exposing a cloud-based virtual machine directly on the Internet. An SSH tunnel can provide a secure path over the Internet, through a firewall to a virtual machine. In 1995, Tatu Ylönen, a researcher at Helsinki University of Technology, designed the first version of the protocol prompted by a password-sniffing attack at his university network; the goal of SSH was to replace the earlier rlogin, TELNET, FTP and rsh protocols, which did not provide strong authentication nor guarantee confidentiality. Ylönen released his implementation as freeware in July 1995, an
The shell game is portrayed as a gambling game, but in reality, when a wager for money is made, it is always a confidence trick used to perpetrate fraud. In confidence trick slang, this swindle is referred to as a short-con because it is quick and easy to pull off; the shell game is related to the cups and balls conjuring trick, performed purely for entertainment purposes without any purported gambling element. In the shell game, three or more identical containers are placed face-down on a surface. A small ball is placed beneath one of these containers so that it cannot be seen, they are shuffled by the operator in plain view. One or more players are invited to bet on which container holds the ball – the operator offers to double the player's stake if they guess right. Where the game is played the operator can win if he shuffles the containers in a way which the player cannot follow. In practice, the shell game is notorious for its use by confidence tricksters who will rig the game using sleight of hand to move or hide the ball during play and replace it as required.
Fraudulent shell games are known for the use of psychological tricks to convince potential players of the legitimacy of the game – for example, by using shills or by allowing a player to win a few times before beginning the scam. The shell game dates back at least to Ancient Greece, it can be seen in several paintings of the European Middle Ages. A book published in England in 1670 mentions the thimblerig game. In the 1790s, it was called "thimblerig" as it was played using sewing thimbles. Walnut shells were used, today the use of bottle caps or matchboxes is common; the swindle became popular throughout the nineteenth century, games were set up in or around traveling fairs. A thimblerig team was depicted in The Derby Day. In Frith's 1895, My Autobiography and Reminiscences the painter-turned-memorialist leaves an account of his encounter with a thimble-rig team: "My first visit to Epsom was in the May of 1856 — Blink Bonnie's year. My first Derby had no interest for me as a race, but as giving me the opportunity of studying life and character it is to be gratefully remembered.
Gambling-tents and thimble-rigging, prick in the garter and the three-card trick, had not been stopped by the police. So convinced was I that I could find the pea under the thimble that I was on the point of backing my guess rather when I was stopped by Augustus Egg, whose interference was resented by a clerical-looking personage, in language much opposed to what would have been anticipated from one of his cloth.'You,' said Egg, addressing the divine,'you are a confederate, you know. Fear of jail and the need to find new "flats" kept these "sharps" traveling from one town to the next, never staying in one place long. One of the most infamous confidence men of the nineteenth century, Jefferson Randolph Smith, known as Soapy Smith, led organized gangs of shell men throughout the mid-western United States, in Alaska. Today, the game is still being played for money in many major cities around the world at locations with a high tourist concentration; the swindle is classified as a confidence trick game, illegal to play for money in most countries.
The game inspired a pricing game on the game show The Price Is Right, in which contestants attempt to win a larger prize by pricing smaller prizes to earn attempts at finding a ball hidden under one of four shells designed to resemble walnut shells. While the ball is not shown during the game, the host shuffles the shells before the start of the game, contestants can win by either winning all four attempts or winning enough attempts, picking the one that has the ball; the shuffling is only allowed before the pricing part of the game begins, once the first small prize is announced, no further shuffling is permitted. Federal game show regulations are designed to ensure the game is a game that can be won. Get-rich-quick scheme Three-card Monte Cups and balls routine Bishop, The Shellgame - For Tableside Tricksters, 2000 Price, The Real Work: Essential Sleight Of Hand For Street Operators, 2001 Whit Haydn and Chef Anton, Notes on Three-card Monte How do big city shell games work?. How Stuff Works
A shell is a payload-carrying projectile that, as opposed to shot, contains an explosive or other filling, though modern usage sometimes includes large solid projectiles properly termed shot. Solid shot may contain a pyrotechnic compound if a spotting charge is used, it was called a "bombshell", but "shell" has come to be unambiguous in a military context. All explosive- and incendiary-filled projectiles for mortars, were called grenades, derived from the pomegranate, so called because the many-seeded fruit suggested the powder-filled, fragmenting bomb, or from the similarity of shape. Words cognate with grenade are still used for an artillery or mortar projectile in some European languages. Shells are large-caliber projectiles fired by artillery, combat vehicles, warships. Shells have the shape of a cylinder topped by an ogive-shaped nose for good aerodynamic performance with a tapering base, but some specialized types are quite different. Solid cannonballs did not need a fuse, but hollow munitions filled with something such as gunpowder to fragment the ball, needed a fuse, either impact or time.
Percussion fuses with a spherical projectile presented a challenge because there was no way of ensuring that the impact mechanism contacted the target. Therefore, shells needed a time fuse, ignited before or during firing and burned until the shell reached its target; the earliest record of shells being used in combat was by the Republic of Venice at Jadra in 1376. Shells with fuses were used at the 1421 siege of St Boniface in Corsica; these were two hollowed hemispheres of bronze held together by an iron hoop. Written evidence for early explosive shells in China appears in the early Ming Dynasty Chinese military manual Huolongjing, compiled by Jiao Yu and Liu Bowen sometime before the latter's death, a preface added by Jiao in 1412; as described in their book, these hollow, gunpowder-packed shells were made of cast iron. At least since the 16th century grenades made of ceramics or glass were in use in Central Europe. A hoard of several hundred ceramic grenades were discovered during building works in front of a bastion of the Bavarian city of Ingolstadt, Germany dated to the 17th century.
Lots of the grenades igniters. Most the grenades were intentionally dumped in the moat of the bastion before the year 1723. An early problem was that there was no means of measuring the time to detonation — reliable fuses did not yet exist and the burning time of the powder fuse was subject to considerable trial and error. Early powder burning fuses had to be loaded fuse down to be ignited by firing or a portfire put down the barrel to light the fuse. Other shells were wrapped in bitumen cloth, which would ignite during the firing and in turn ignite a powder fuse. Shells came into regular use in the 16th century, for example a 1543 English mortar shell was filled with'wildfire'. By the 18th century, it was known that the fuse toward the muzzle could be lit by the flash through the windage between the shell and the barrel. At about this time, shells began to be employed for horizontal fire from howitzers with a small propelling charge and, in 1779, experiments demonstrated that they could be used from guns with heavier charges.
The use of exploding shells from field artillery became commonplace from early in the 19th century. Until the mid 19th century, shells remained as simple exploding spheres that used gunpowder, set off by a slow burning fuse, they were made of cast iron, but bronze, lead and glass shell casings were experimented with. The word bomb encompassed them at the time, as heard in the lyrics of The Star-Spangled Banner, although today that sense of bomb is obsolete; the thickness of the metal body was about a sixth of their diameter and they were about two thirds the weight of solid shot of the same caliber. To ensure that shells were loaded with their fuses toward the muzzle, they were attached to wooden bottoms called sabots. In 1819, a committee of British artillery officers recognized that they were essential stores and in 1830 Britain standardized sabot thickness as a half inch; the sabot was intended to reduce jamming during loading. Despite the use of exploding shell, the use of smoothbore cannons firing spherical projectiles of shot remained the dominant artillery method until the 1850s.
The mid 19th century saw a revolution in artillery, with the introduction of the first practical rifled breech loading weapons. The new methods resulted in the reshaping of the spherical shell into its modern recognizable cylindro-conoidal form; this shape improved the in-flight stability of the projectile and meant that the primitive time fuzes could be replaced with the percussion fuze situated in the nose of the shell. The new shape meant that further, armor-piercing designs could be used. During the 20th Century, shells became streamlined. In World War I, ogives were two circular radius head - the curve was a segment of a circle having a radius of twice the shell caliber. After that war, ogive shapes became more elongated. From the 1960s, higher quality steels were introduced by some countries for their HE shells, this enabled thinner shell walls with less weight of metal and hence a greater weight of explosive. Ogives were further elongated to improve their ballistic performance. Advances in metallurgy in the industrial era allowed for the construction of rifled breech-loading guns that could fire at a much greater muzzle velocity.
After the British artillery was shown up in the Cri
A concrete shell commonly called thin shell concrete structure, is a structure composed of a thin shell of concrete with no interior columns or exterior buttresses. The shells are most flat plates and domes, but may take the form of ellipsoids or cylindrical sections, or some combination thereof; the first concrete shell dates back to the 2nd century. Most concrete shell structures are buildings, including storage facilities, commercial buildings, residential homes. Concrete shell construction techniques are well suited for complex curves and are used to build boat hulls, it was used by the British to create the Mulberry Harbours for the 1944 D-Day invasion of Normandy. Like the arch, the curved shapes used for concrete shells are strong structures, allowing wide areas to be spanned without the use of internal supports, giving an open, unobstructed interior; the use of concrete as a building material reduces both materials cost and construction costs, as concrete is inexpensive and cast into compound curves.
The resulting structure may be immensely safe. Since concrete is a porous material, concrete domes have issues with sealing. If not treated, rainwater can leak into the interior of the building. On the other hand, the seamless construction of concrete domes prevents air from escaping, can lead to buildup of condensation on the inside of the shell. Shingling or sealants are common solutions to the problem of exterior moisture, dehumidifiers or ventilation can address condensation; the oldest known concrete shell, the Pantheon in Rome, was completed about AD 125, is still standing. It has a massive concrete dome 43m in diameter, with an oculus at its centre. A monolithic structure, it appears to have been sculpted in place by applying thin layers on top of each other in decreasing diameter. Massively thick at the bottom and thinning at the top, the Pantheon is a remarkable feat of engineering. Modern thin concrete shells, which began to appear in the 1920s, are made from thin steel reinforced concrete, in many cases lack any ribs or additional reinforcing structures, relying wholly on the shell structure itself.
Shells may pre-cast off site and moved into place and assembled. The strongest form of shell is the monolithic shell, cast as a single unit; the most common monolithic form is the dome, but ellipsoids and cylinders are possible using similar construction methods. Geodesic domes may be constructed from concrete sections, or may be constructed of a lightweight foam with a layer of concrete applied over the top; the advantage of this method is that each section of the dome is small and handled. The layer of concrete applied to the outside bonds the dome into a semi-monolithic structure. Monolithic domes are cast in one piece out of reinforced date back to the 1960s. Advocates of these domes consider them to be cost-effective and durable structures suitable for areas prone to natural disasters, they point out the ease of maintenance of these buildings. Monolithic domes can be built for other purposes. Completed in 1963, the University of Illinois Assembly Hall, located in Champaign, Illinois was and is the first concrete-domed arena.
The design of the new building, by Max Abramovitz, called for the construction of one of the world’s largest edge-supported structures. See Construction of Assembly Hall; the Seattle Kingdome was the world's first concrete-domed multi-purpose stadium. It was completed in 1976 and demolished in 2000; the Kingdome was constructed of triangular segments of reinforced concrete. Thick ribs provide additional support. Thin-shell structure Pier Luigi Nervi Eduardo Torroja Heinz Isler Félix Candela Seaplane Hangars in Seaplane Harbour, Estonian Maritime Museum in Tallinn, Estonia, ex-Peter the Great's Naval Fortress Mark Ketchum's Concrete Shell page Historic Preservation of Thin-Shell Concrete Structures - Includes case studies of the Seattle Kingdome and MIT's Kresge Auditorium, both concrete dome structures. Heinz Isler in Structurae web page Heinz Isler in Princeton University Art Museum
A bivalve shell is part of the body, the exoskeleton or shell, of a bivalve mollusk. In life, the shell of this class of mollusks is composed of valves. Bivalves are common in all aquatic locales, including saltwater, brackish water, freshwater; the shells of bivalves wash up on beaches and along the edges of lakes and streams. Bivalves by definition possess two shells or valves, a "right valve" and a "left valve", that are joined by a ligament; the two valves articulate with one another using structures known as "teeth" which are situated along the hinge line. In many bivalve shells, the two valves are symmetrical along the hinge line— when symmetrical, such an animal is said to be equivalved. If symmetrical front-to-back, the valves are said to be equilateral, are otherwise considered inequilateral; this exoskeleton serves not only for muscle attachment, but for protection from predators and from mechanical damage. The shell has several layers, is made of calcium carbonate precipitated out into an organic matrix.
It is secreted by a part of the molluscan body known as the mantle. The shells of bivalves are equal sides connected by a hinge. Bivalve shells are collected by professional and amateur conchologists and are sometimes harvested for commercial sale in the international shell trade or for use in glue, chalk, or varnish to the detriment of the local ecology; the bivalve shell is composed of two calcareous valves. The mantle, a thin membrane surrounding the body, secretes the shell valves and hinge teeth; the mantle lobes secrete the valves, the mantle crest creates the other parts. The mantle itself is attached to the shell by numerous small mantle retractor muscles, which are arranged in a narrow line along the length of the interior of the shell; the position of this line is quite visible on the inside of each valve of a bivalve shell, as a shiny line, the pallial line, which runs along a small distance in from the outer edge of each valve joining the anterior adductor muscle scar to the posterior adductor muscle scar.
The adductor muscles are. In some bivalves the mantle edges fuse to form siphons, which take in and expel water during suspension feeding. Species which live buried in sediment have long siphons, when the bivalve needs to close its shell, these siphons retract into a pocket-like space in the mantle; this feature of the internal anatomy of a bivalve is indicated on the interior of the shell surface as a pallial sinus, an indentation in the pallial line. The valves of the shell are made of either calcite or both calcite and aragonite with the aragonite forming an inner layer, as is the case with the Pterioida which have this layer in the form of nacre or mother of pearl; the outermost layer of the shell is known as the periostracum and is composed of a horny organic substance. This sometimes forms a brownish "skin" on the outside of the shell; the periostracum may start to peel off of a shell when the shell is allowed to dry out for long periods. The shell is added to, increases in size, in two ways - by increments added to the open edge of the shell, by a gradual thickening throughout the animal's life.
The two shell valves are held together at the animal's dorsum by the ligament, composed of the tensilium and resilium. In life the ligament opens the shell, the adductor muscle or muscles close the shell; when a bivalve dies, its adductor muscle relax and the resilium pushes the valves open. A few groups of bivalves are active swimmers like the scallops. In many species of cemented bivalves, the lower valve is more cupped than the upper valve, which tends to be rather flat. In some groups of cemented bivalves the lower or cemented valve is the left valve, in others it is the right valve; the oldest point of a bivalve shell is called the beak, the raised area around it is known as the umbo. The hinge area is the back of the shell; the lower, curved margin is the ventral side. The anterior or front of the shell is where the byssus and foot are located and the posterior or back of the shell is where the siphon is located. Without being able to view these organs, determining anterior and posterior can be rather more difficult.
In those animals with a siphon, the pallial sinus of the siphon, which will be present on both the left and right valves, will point towards the animal's posterior— such valves are called sinopalliate. Shells without a pallial sinus are termed integripalliate— such animals have a byssal notch present on the anterior end of the right valve, the anterior auricles or "wings" of both valves will be either larger than, or equal to, the posterior ones; such valves may have a distinctive "comb" or ctinoleum within the byssal notch on the right valve. If a valve has neither notch nor comb nor sinus, and