8 CYCLADID^, 



Isis, Cherwell, Mersey^ Foss, and other streams in 



Yorkshire, &c. 



C. CORNEA. Linnceus. PI. I, fig. o and PI. VIII, fig. 8. 



Shell subglobose, slightly striated concentrically; umbones obtuse; 

 ligaments indistinct. 



Tellina cornea, Linn, Penn. Cylas rivalis, Drap. 

 Tellina rivalis. Mull. Cardium corneum, Pult., 8fc. 



The shell of this widely-distributed Cyclas is rather 

 thin, and very finely striated. The valves are much 

 sv/oUen in specimens that are fully formed , and of a 

 fawn colour ; younger ones a dirty yellow. Length 

 half an inch, and breadth five-twelfths. Tubes of the 

 animal slightly tinged with flesh colour, foot and 

 mantle white. 



Hah. Abundant in almost every district, inhabiting 

 slowly-running streams and sometimes stagnant ponds. 



C. CALicuLATA. Drapamaud. PI. I, fig. 4. 



Shell rather rhombic, umbones prominent, capped. 

 Cyclas lacustris, Turt, Gray, ^c. Tellina lacustris, 

 Linn. Cardium lacustris, Mont. 



The prominent umbones and extremely fragile char- 

 acter of this species, will readily distinguish it from its 

 congeners. The surface is glassy, of a greyish ash 

 colour, and the valves much more compressed than in 

 C. cornea. We have found specimens of this shell one 

 third of an inch long and five-twelfths broad, but they 

 are commonly rather smaller. 



Hab. It is by no means an abundant species, but 

 seems to be more plentiful in the north than the south 

 of England. It inhabits stagnant pools and ditches. 



C. LACUSTRIS. Draparnaud. PL I, fig. 5. 



"Shell subrhombic, elongate, ovate, thin, inequilateral, and rather 

 compressed, especially below, where the valves meet each other at an 

 acute angle; a little swollen behind the umbones." 



A large individual measured five lines in length, and 

 seven in breadth. The general appearance of the 

 species is that of a greatly produced caliculata. but de- 

 void of the characteristic beaks. 



