25 



The Conchas are divided into Fluviatiles and Mari-nae. 



CONCHJE FLUVIATILES. 



The shells covered with a false epidermis, and having two 

 lateral teeth near the hinge. 



CYCLAS. 



GESERIC 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 

 Cycladae is, the shell subcordate, porcellaneous, thin, 

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

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



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

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

 Brit., vol. 1, p. 86. C. C. Flem. 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. 



GEXERIC CHARACTER: The shell suboval, wedge- 

 shaped, unequal sided ; the teeth as in Cyclas. 



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

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

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

 Falmouth. 



CONCHjE 31ARINJE. 

 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 of the 

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

 Ligament external, partly sunk under the beaks. 

 By having an epidermis, and their sometimes almost 



obsolete lateral tooth, the Cyprinee are somewhat allied to 



the fresh water Concha?. 



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

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



E 



