378 



MOLLUSCA. 



The species of Cardia are numerous on our coasts, and the C. edule, Linn., is gathered for food. [Fossil species 

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



We may separate from them, under the name of Hemicardia, the species with valves compressed from before 

 backwards, and strjngly keeled in the middle, for it is difficult to believe that the animal is not modified to suit 

 this singular configuration. 



The Donaces (Donax, Linn.) — 



Have nearly the same kind of hinge as the Cardia, but their shell is of a very different form, being a 

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

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

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

 animal (Peron&a, Poli) is furnished with long tubes, that are received into a sinus of the mantle. 



We have some native examples. (The Donax irregularis, a fossil from the neighbourhood of l)ax, is the type of 

 the genus Gratelupia of Desmoulins, and is distinguished from the other Donaces by several tooth-like lamellae 

 which accompany the hinge teeth.) 



The Cyclades, Brug., — 

 Like the Cardia and Donaces, have two teeth in the middle of the hinge, and before and behind two 

 prominent and sometimes crenulated laminae ; but the shell, 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 (Tellina cornea, Linn.) is very common in our marshes. 



Cyrena, Lam.— The shell is thick, somewhat triangular and oblique, and covered with an epidermis, and is 

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

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

 tooth behind : under the teeth a large fossa, in which is lodged a part of the ligament. Palath&a, Brug., [Pota- 

 mophila, Sowerby,] 1ms 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 [Venus subviridis, 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 Corbis, Cuv. (Fimbria, 

 Megerl.) Marine transversely oblong shells, which 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 funbriata, Linn., is the type.] Since the impression of the cloak has no fold, the tubes 

 ought to be short. There are some fossil species. 



The Tellinidje (TeUina, Lin.) — 

 Have in the centre [of the hinge] a tooth on 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 that part, where they gape a little.* The animal (Peroncea, 

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

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

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

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

 course of the transverse stria?. 'We could separate generically some oblong species, which have no 

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

 Tellinides, Lam. 



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

 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 very long) towards the nates. The 

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



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

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

 without an impress of the retractor muscle of the tube, but that of the anterior retractor muscle 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 Ongulina, which has an orbicular shell, two hinge teeth, but no lateral 

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



* ['* The irregular flexuosity of the (interior ventral margin appears 

 to have been constantly regarded as the principal distinguishing cha- 

 racter of this beautiful genus; and when we consider the number of 



species possessing this character, and agreeing also in other general 

 circumstances, it may perhaps be still considered as the essential 

 character of the genus.'' — Sowerby.] 



