14 



3. Cyclas calyculata. Shell rliombic-orbicular, flat- 

 tish, transparent, nearly smooth, a little angular 

 on one side, with the beaks very prominent and 

 tubercular. 



Cyclas caliculata. Drap. p. 130. t. 10./. 14, 15. 



Cyclas lacustris. Turton, Dith. p. 249. «. 11./. 18. 



Tellina lacustris. Wood, p. 197. pi. 45./ 5. 



Cardium lacustre. Montagu, p. 89. 



Shell about the size of the former, but is of a flat 

 form, a blueish-white colour, nearly smooth, and 

 lias tubercular appendages on the beaks. 



In lakes and still waters, but not common. 



A variety is found, more opake, with the beaks of a 

 blackish colour, and not so prominent. It is called 

 Cyclas stagnicola by Dr. Leach. 



4. Cyclas lacustris. Shell rhombic-orbicular, flat- 

 tish, striolate, a little angular on one side ; with 

 the beaks depressed and not tubercular. 



Cyclas lacustris. Drap. p. 130. t. 10./ 6, 7. 



In its outline it very much resembles the last, but is 

 of a more opake and dark gray colour, and has no 

 tubercles on the beaks. 



In stagnant waters, not common. 



