14 



3. CYCLAS calyculata. Shell rhombic-orbicular, flat- 

 tish, transparent, nearly smooth, a little angular 

 on one side, with the beaks very prominent and 

 tubercular. 



Cyclas caliculata. Drap. p. 130. 1. 10. f. 14, 15. 



Cyclas lacustris. Turton, Dith. p. 249. t. II. f. 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 

 has 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. 1. 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. 



