378 MOLLUSCA. 



Tlie species of Carrtia are numerous on our coasts, and the C. edide, Linn., is g:athered for food. [Fossil species 

 occur in nearly all the fossiliferous beds, from the mountain limestone upwards.] 



\A'e may separate from them, under tlie name of Hemicardia, the species with valves compressed from befo; '^ 

 backwards, and strjng^ly keeled in the middle, for it is ditficult to believe that the animal is not modified to suit 

 this singular confisn^iration. 



TuFi DoNACES {Dona.r, Linn.) — 



Have nearly the same kind of liingc as tlie Cardia, bat their shell is of a veiy different forri], being a 

 triangle, of which the obtuse angle is at tlie summit of the valves, and the base at their edge, and of 

 which the shoftest side is that of the ligament, or the posterior side, a rare circumstance among 

 Bivalves. Tlipy are generally small shells, prettily striated from the beaks to the margins. Their 

 animal {Pero7)cea, Poii) is furnished "with long tubes, that are received into a sinus of the mantle. 



We have some native exanjples. (The Donni- irregularis, a fossil from the nei;;hbourhood of Uax, is the type of 

 the i;;enus G;'ff^c/^//i/iT of Desmoulins, and is distinf^uished from the other Donaces by several tooth-like lamella; 

 "which accompany the hint^'^e reetli.) 



The Cyclades, Brug., — ■ 

 Like the Cardia and Uonaccs, have twn iceih in the middle of the hinge, and before and behind two 

 promiuent ami sometimes crenulated !aniiu;c ; but the ^hell, as in several species of Venus, is more or 

 less rounded, equilateral, and transversely striated. The external tint is usually grey or greenish. The 

 animal has moderate tubes, and is an inhabitant of fresh waters. 



One species [TciVnta cornea, Linn.) is very common in our marshes. 



Ci/reim, Lam.— The shell is thick, somewhat triangular and oblique, and covered with an epidennis, and is 

 further distinguished from the Cyclas by having three hinge teeth. They likewise inhabit rivers, but we have 

 none in France. Cypr'uia, Lam. — Shell thick, oval, with curved beaks, three strong teeth, and besides, a lateral 

 tooth beliind : under the teeth a large fossa, in which is lodged a part of the ligament. Palathcea, Brug., \_Poia' 

 rnoj'Iiihi, Sowerby,] has the shell a right-angled triangle ; three teeth in one valve and two in the other, diverging 

 from the beaks ; and the lateral teeth approximated. The single species known [_ye7uis subviridh^ Gmel.] is from 

 the fresh waters of India. [It is also found in the river Congo.] 



This is the proper place to set another genus dismembered from the Venus, viz., the Corh'is, Cuv. {Fimbria, 

 Megerl.) Marine transversely oblong shells, whicli have also strong middle teeth and well marked lateral plates : 

 their external surface is furnished with transverse ribs, so regularly crossed by rays that it may be compared to 

 ■wicker-work. \^Venus fimbriata, Linn., is the type.] Since tlie impression of the cloak has no fold, the tubes 

 ought to be short. There are some fossil species. 



The Teluxtd-E {TeUina, Lin.) — 

 Have in the centre [of the hinge] a tooth ou the left and two teeth on the right, often bifid, and at 

 some distance in front and behind ; on the right valve, a lateral tooth or plate, which does not pene- 

 trate into a cavity of the opposite one. There is a slight fold near the posterior extremity of both 

 valves, which renders them unequal in tliat part, where they gape a little.* The animal [Peroncea, 

 Poll), like that of Donax, has two long tubes, respiratory and excrementitial, which can be withdrawn 

 into the shell, and concealed in a duphcature of the cloak. The shells are generally transversely 

 striated, and painted with beautiful colours. Some arc oval and thickish ; others oblong and much 

 compressed ; others lenticular. Instead of a fold, we often lind in the latter merely a deviation in the 

 course cf the transverse stride. "We could separate gencrically some oblong species, which have no 

 lateral teeth ; and others that, with the hinge of a Tellina, have no posterior fold, form the genus 

 Tellinidc's-, Lam. 



It is necessary to distinguish from Tellina the Loripes, Poli, which have a lenticular shell with the central tectli 

 almost obsolete, and behind the nates a simple groove for the ligament. The animal has a short double tube, and 

 its foot is prolonged into a cylindrical cord. We notice within the valves, besides the ordinary impressions, a 

 mark going obliquely from the impression of the anterior muscle (which is veiy long) towards the nates. The 

 impression of the qloak exhibits no sinus for the retractor muscle of the tube. 



Lucina, Brug., has, like Cardium, Cyclas, &c., separate lateral teeth penetrating between corresponding lamina; 

 of the other valve ; and in the centre are two teeth, which are often scarcely visible. The shell is orbicular, 

 without an imjfress of the retractor muscle of the tube, but that of the anterior retractor nmscle is very long. 

 Having thus the same marks as Loripes, their animals ought to be analogous. [It is obvious that Loripes and 

 Lucina are but one and the same genus.] The recent species, so far as is known, are much less numerous than 

 the fossil : the latter are very common in the vicinity of Paris. 



We ought to place near the Lucina the Ongidina, which has an orbicular shell, two hinge teeth, but no lateral 

 Dues, arid the anterior muscular impression is not so long. 



• [" The irrc'iiular flesuosily ni the untt'rior vcritml mirjriri appears 1 spcciiis posscashif; this cliaracttT, nuA QfreciiitT "I'^u i'] ntlier goni.Tiil 

 lo liave been constiintly regarded as tin; priucipiil diBtinnuisliiti^; cha- circumstaners, it may ptrhaps lie sUU coiisiilcrfd as the csscniiiii 

 ractLT of tliia beautiful k''""!* s and when we coii.sider tliu number of 1 character uf tbe (^eiius." — Suwerby.] 



