ACBPHALA TESTACEA. 103 



these same summits there is ahuost always an oval impression termed 

 the anwi or lunula*. 



The animal is always furnished with two more or less px'otractile 

 tubes, sometimes 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 them — the AsTARTyE, Sowerb., or Crassin^, Lam., — have 

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

 in their thickness and some other characters J. 



Amc'iig the cordiform species, that is, those which are shorter and 

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

 we should remark those where the plates or transverse stri?e terminate 

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

 crests elevated behind. 



We subsequently and gradually come to the Cythere^, Lam., 

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

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



Some cf them have an elliptical and elongated form^ ; others are 

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

 brated species (Venus Dione, L., Chemxn., 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 

 forms a large and almost rectilinear triangle \\. 



When their animals are better known, Ave shall most probably 

 have to separate from the Cytherese, 



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

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

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



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



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

 extremity of the shell, which corresponds to the true anus of the animal, to be 

 styled 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 summits. 



t Venus Ullerala, Chemn., VII, xli ; — V. rotunda, lb., xlii, 441 ; — F. texHUs, lb., 

 442 ; — V. decussafci, xliii, 456 ; &c. 



+ Fenus scoHca, Hans Lerin, VIII, tab. 2, f. 3 ; — Crassina clanmoniemis, Lam. ; 



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



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



§ Fenus dijsera, Chemn., VI, 27, 299 ; — Fen. plicata, Encyc. pi. 275, 3, a, h ; — 

 Fen crehisuUca, lb., f, 4, 5, 6. 



II Venus puerpera, Encyc, 278 ; — Fen. co7-bis, Lam., Encyc. pi. 276, f. 4. 



^ Fenus yicjanfea, Encyc, 28,3; — Fen. chione, Chemn., VI, 32, 343; — Fen. 

 enjcina, lb., 347 ; — Fen. maculata, lb., 33, 345. 



** Fen. meretrix ; — Fen. lusoria ; — Fen. castrensis. 



ft Fenus exolela, Chemn., VII, 38, 404 — the genus Orbiculus, Megerle. 



XX Fen. scripta, Chemn., VII, 40, 422. 



