ACKPHALA TESTACEA. 103 



.inmits thnv is almost always an oval impression termed 

 tli- tuiii* or tunula*. 



Tin- animal is always furnished with two more or less protractile 

 tulx-s. MMiietiiw-s united, and with a compressed foot, which enable it 

 to crawl. 



M. Lamarck appropriates the name of VENUS to those which have 

 three small diverging teeth under the summit. This character is 

 particularly well marked in the oblong and slightly convex spe- 

 cies f. 



Some of tin-in the ASTARTA, Sowerb., or CRASSINJS, Lam., have 

 only two diverging teeth on the hinge, and approach the Crassatellae 

 in their thickness and some other characters J. 



Among the cordiform species, that is, those which are shorter and 



have more convex nates, and with more closely approximated teeth, 



\\v >h<uld remark those where the plates or transverse striae terminate 



in crests or tuberosities ||, and those that have longitudinal ribs and 



s elevated behind. 



\\V subsequently and gradually come to the CYTHEREJE, Lam., 

 which have a fourth tooth on the right valve, projecting under the 

 la nu la, and received into a corresponding cavity in the right one. 



Some of them have an elliptical and elongated form U ; others are 

 convex**, and it is among these latter that we must place a cele- 

 Imited species (Venus Dione, L., Chemn., VI, 27, 271), from whose 

 form originated the application of the name Venus to the genus. 

 Its transverse plates terminate behind in salient and pointed spines. 



There are some species of an orbicular form, and with slightly 

 hooked summits, in which the impression of the retractor of the tubes 

 terms a large and almost rectilinear triangle ff. 



When their animals are better known, we shall most jrobably 

 have to separate from the Cythereae, 



1. Those species of a compressed lenticular form, in which the 

 nates are united into a single point. The fold of the contour of the 

 mantle is wanting, and shows that their tubes are not protractile JJ : 



2. Those of a convexly orbicular form, in which the fold is not 



* These fantastic appellations of vulva and onus, have probably caused the 

 i \trrinit\ of the shell, which corresponds to the true anus of the animal, to be 

 -tyli-d the anterior, and that where the mouth is situated, the posterior. We have 

 restored to these extremities their true denominations. We must recollect that the 

 ligament is always on the posterior side of the summit-. 



f / VJIIM lilterata, Chemn., VII, xli ; F. rotunda, Ib., xlii, 441 ; V. lextilis, Ib., 

 442 ; V. decussata, xliii, 456 ; &c. 



J Venus scotica, Hans Lerin, VIII, tab. 2, f. 3 ; Crassina danmoniensis, Lam. ; 

 and among the fossil species, Ast. lucida, Sower., Min. Conch., II, pi. 137, f. 1 ; 

 I '. Osmalii, Lajonkere, Soc. d'Hist. Nat. de Paris, I, tab. 6, f. 1. 



Venus dysera, Chemn., VI, 27, 299 ; Ven. plicata, Encyc. pi. 275, 3, a, b , 

 Ven frcbisulica, Ib., f, 4, 5, 6. 



|| IVuNt puerpera, Encyc., 278 ; Ven. corbu, Lam., Encyc. pi. 276, f. 4. 



f Venus gigantea, Encyc., 28,3; Ven. chione, Cbcinn., VI, 32, 343; Ven. 

 i',.,347; Vem. maculnf- . ,15. 



Ven. meretrir , / ctulrtnsis. 



ft Venus exoleta, Chemn., VII, 38, 404 the gcuus OABICULUS, Megeile. 



H I'm. scriplu, Chemn., VII. to, 422. 



