380 MOLLUSCA. 



at^apc at botli extremities. TLey live almost uniformly ouried in sand or mud, in rocks or in 



wood. 



The j\1yai)/e {J\h/a, Linn.) — 



Are hlvalved slirlls with a variable hinge. Tlic dmihle liilie forms a fleshy cylinder; the foot is com- 

 ]itrsM'ii. Vr(jm variations in the hinge MM. I'aiidin, Lamarck, &c., have established the following 

 sididivisions, the first three having an internal ligament. 



Liitraria, Lam.— The hp;ament, like that of the Mactra, is inserted in a lar^e trian^ukir fossa in each valve, ami 

 in front of that fossa is a small tooth en chevron, but there are no lateral teeth. The ^^ape of tlie valves is wide, 

 particularly at the posterior end, whence the large douhle tube for respiration and excremential matters protrudes. 

 'l"\je foot, which issues at the opposite end, is small and compressed. The species burrow in sand at the mouth of 

 nvcrs. 



J/v(7, Lam., bns in one valve a broad, spoon-shaped tootb, which projects into the other valve, in which tliere 

 is a fossa, and the lij^ament is stretched from the fossa to the tooth. The species on our shores burrow in sand. 

 Near to theMys we ought to place \.\\e Anatime^ Lam., that have a small moveable testaceous appendage, connected 

 _^ with the ligament immediately before the hinder teeth. In the Solcmya, Lam., the 



v'^-f^('''Vv^v^i:^ ligament appears externally, but a portion of it remains attached to a spoon-shaped 



^ ' '^^^^"n^fVij tooth in each valve. There is no other tooth in the hinge. A thick epidermis overlaps 



''-^' -' l-''/y the margins of the shell. An example (Tc////;^ loijnta, Poll) lives in the Mediterranean. 

 ITlie animal is so remarkable that it may become the type of a distinct family, for, 

 instead of four lamellar branchiae, it has two only, which are pectinate, or rather pen- 

 nate.] Glijcymeris, Lam. {Crt/todaina, Daud.), has neither teeth, nor laminae, nor 

 fosst-e, in the hinge, but a simple callosity, behind which there is an extei'nal ligament. 

 The animal is similar to Mya. The best known species {Mi/a siUqna, Linn.), comes 

 from the Arctic seas. Panopca, Mesnard, Lagr., have in front of tlie callosity of the 

 Fiir. !','L> — .siLutKin sui-,ro3trjita pieccding, a strong tooth immediately under the beak, which crosses with a similar tooth 

 of tlie opposite valve, — a character which alfines them to Solen. There is a large species from the hills at the foot 

 of the Apennines, so well preserved that it has been sometimes believed to have been brought from the sea. Per- 

 haps we ought to remove from the genus another fossil species, which is almost completely closed at the anterior end. 

 \\'(j ma\ ;irr;im;e at the end of these diflerent moditications of the Myadte, the Pandora^ Brug., which has one 

 \al\e much flutter than the other, an internal ligament placed crosswise, accompanied with a projecting tui.ttli of 

 the flat valve. The posterior side of the shell is elongated. The animal is more completely contained w iiliin (he 

 shell than it is in the preceding genera, and the valves close better, but its li;ibits are the same. Uuc n.iti\ i- .^[lecies 

 (Ti'Ui)ia inoiiiiiivalvis, Chemn.), is well known. 



Here, also, we group together some small but singular genera. The Byssomia, Cuv., characterized by an oblong 

 tuuthless shell, with the opening for the ftiot very nearly in the centre of the valves, and opjiosite the beaks. They 

 perforate rocks and corals. *")ne species, furnished with a byssus {^Jylihis ji/ictmlis, Mull.), is \ery numerous in 

 the seas of the north. IJ/u/elhr, Daud., has a shell that gapes in the middle when- Ihe fuot pmtrndes, asm the pre- 

 rciling, but the tooth of the hinge is more distinct. The shell is often armed backwards with [t\io] rows of spines. 

 The Specie.^ live in sand and amid zoophytes, &c. The northern seas possess a small species.* 



The Solenes {Solen, Linn.) — 

 Have an oblong or elongated bivalved shell, but their liinge is always fiirni^licd with distinct teeth, and 

 their ligament is always external. 



Solen, Cuv., or Pazor-fi^h, has a shell iri the form of an elongated cylinduv, w ith two or three teeth in each valve 

 towards the anterior extremity, where the foot passes out. This is of a conical shape, and is used by the animal 

 to form its burrow in the sand, in which it sinks rapidly on the approach of danger. Several species inhabit our 

 sliores. The species in which the teeth approach near the centre of the shell may be distinguished generically. 

 Tlie shell in some of them is still long and straight; in others it is wider and shorter, and the foot of these is very 

 large. Some such are found in the Mediterranean. In the Sangninolaria, Lam., the hinge is very nearly the same 

 as in the broad Solenes, and there are two liinge teeth at the middle of each valve ; but the valves approximate 

 much closer at their ends, where they only gape to a slight extent, as in some of the Mactra- : iS. rosea is the type. 

 I'sammobia, Lam., differs from Sanguinolaria in having a single tooth in one valve, which clasps in between two of 

 the opposite ones. And the Psammoihea, Lam., have only one tooth in each valve, but otherwise resemble 

 Psammobia. [The Glauconome, Gray, is a genus of the family Solenacete, " inhabiting some of the great rivers of 

 the continent of China." The shell is thin, oblong, with close margins, and three teeth in each valve. Solenella, 

 .Suwerby, is an interesting genus, partaking of the characters of Nucula and Solen, so that it may be regarded as 

 the link that connects the two families Solenacece and Mactracea:. "It belongs to the Solenacea?, having the external 

 ligament and the large sinus in the muscular impression of the mantle ; but resembh'S Nucula in ha\'ing the laterat 

 teeth divided into a series of minute and pointed teeth, dilTeiiug from it, however, in not having an internal 

 ligament." The species are South American.] 



The Pholades {Pholas, Linn.), — 

 Have two principal valves, wide and ventrieosc on tlic side of the mouth, narrowed and chiiigatcd on 

 the oiijiositc side, and leaving at each end a large oldicpic oi>Gniiig ; tlie hinge has, iikc that uf the M\a, 



• [Byr,srj„iii,. Ilinri llii, Bi.i|.l,,,liiis, mi-l Phokohins of Lcnrh, iirc n\i rcHuccd to tlic ^■.iiml-i'-i of Lniu,, hy Si>M'(Tl,-y, rui.i mil .u,re.isoii-,lily.j 



