25 



The Conchee are divided into Fluvialiles and Marina?. 



CONCEDE FLU VI A TIL ES. 



The shells covered with a false epidermis, and having two 

 laieral teeth near the hinge. 



CYCLAS. 



GENERIC CHARACTER: Shell ovate, globose, trans- 

 verse; equalvalved, the beaks tumid; cardinal teeth very 

 small, sometimes scarcely perceptible; occasionally two 

 in each valve, one of them plaited in two ; sometimes only 

 one plaited or lobed tooth in one valve, and two in the 

 other; lateral teeth transversely elongated, compressed, la- 

 mellar. Ligament external. Mr. Gray's character of his 

 Cyclada? is, the shell subcordate, porcellaneous, thin, 

 covered with a hard, olive, horny periostraca ; hinge teeth 

 two or three, diverging; lateral teeth distinct, laminar. 



C. CORNEA. TelSina Cornea. Turt. Lin. Pen. Brit. 

 Zo., vol. 4, pi. 49, fig. 33. Cardium C. Mont. Test. 

 Brit., vol. 1, p. 80. C. C. Fieni. Brit. An., p. 452. 

 Gray's Turton's Manual of land and fresh water shells, 

 p. 280, pi. 1, fig. 2. There are few situations in Cornwall, 

 in which the Cycladae can find a proper habitation ; and 

 hence the present species is in a great measure local. I 

 have obtained it, by favour of a Lady, from near Helston. 



PISIDIUM. 



GENERIC CHARACTER: The shell suboval, wedge- 

 shaped, unequal sided ; the teeth as in Cyclas. 



P. AMNICUM. Cardium A. Mont. Test. Brit., vol. 1, 

 p. 86. Cyclas A. Flem. Brit. An., p. 453. P. A. 

 Gray's Turt., p. 285, pi. 1, fig. 5. In the Swanpool, near 

 Falmouth. 



CONCH JE MARINJE. 

 Generally with no lateral teeth : sometimes the whole 

 shell, except the beaks, covered with epidermis. 



CYPRINA. 



GENERIC CHARACTER ; The valves equal, the shell 

 obliquely heartshaped, the beaks obliquely curved. Three 

 unequal cardinal teeth, approaching at their base, slightly 

 diverging above. One lateral tooth, distant from the binge, 

 on the anterior side, sometimes obsolete. Callosities ot the 

 Nymphae large, arched, ending near the beaks by a pit. 

 Ligament external, partly aunk under the beaks. 

 By having au epidermis, and their sometimes almost 



obsolete lateral tooth, the Cyprinae are somewhat allied to 



the fresh water Conchas. 



* C. ISLANDJCA. Venus I. Turt. Lin. V. Mercenaria 

 Pen. Bi it. Zo., vol. 4, pi. 53, fig. 47. V. I. Mont. Test. 



E 



