280 MOLLUSCA. 



shortest side is that of the ligament, or the posterior side, a rare circum- 

 stance in this degree, among bivalves. They are generally small, and pret- 

 tily striated from the summits to the edges; their animal PEROIOSA, Poll, 

 is furnished with long tubes which are received into a sinus of the mantle. 

 The 



CYCLAS, Brug. 



Separated from Venus by Brugieres, like the Cardia and Donaces, has two 

 teeth in the middle of the hinge, and before and behind, two salient and 

 sometimes crenulated plates; but the shell, as in several species of Venus, is 

 more or less rounded, equilateral, and transversely striated. The animal 

 has moderate tubes. The external tint is usually grey or greenish. The 

 Cyclades inhabit fresh water. 



CORBIS, CllV. 



Marine testaceous Acephala, transversely oblong, which have also stout 

 middle teeth, and well marked lateral plates; their external surface is fur- 

 nished with transverse ribs so regularly crossed by rays, that it may be com- 

 pared to wicker-work. In the 



TELLINA, Lin. 



There are in the middle, one tooth on the left and two teeth on the right, 

 frequently forked, and at some distance before and behind, on the right 

 Talve, a plate, which does not penetrate into a cavity of the opposite one. 

 There is a slight plica near the posterior extremity of the two valves, which 

 renders them unequal in that part, where they are somewhat open. 



The animal of the Tellinx PEB.OBTJEA, Poli, like that of the Donaces, 

 has two long tubes, which withdraw into the shell, and are concealed in a 

 duplicature of the mantle. 



Their shells are generally transversely striated, and decorated with beau- 

 tiful colours. 



LUCINA, Brug. 



Separated lateral teeth, as in the Cardia, Cyclades, &c., that penetrate be- 

 tween the plates of the other valve; in the middle are two teeth, frequently, 

 but slightly apparent. The shell is orbicular, and without any impression 

 of the re tractor muscle of the tube; that of the anterior constrictor, however, 

 is very long. 



The living species are much less numerous than those that are fossil; the 

 latter are very common in the environs of Paris. 



VENUS, Lin. 



This genus comprises many Testacea whose general character consists in 

 the teeth and plates of the hinge being approximated under the summit, in 

 a single group. They are usually more flattened and elongated, in a direc- 



