13 



This is the largest species of the family, sometimes 

 measuring three quarters of an inch in breadth. 

 It is covered with a dark horny-green epidermis, 

 under which it is dead white : the striae are very 

 fine, and elegantly disposed ; and it is frequently 

 marked with paler transverse zones ; the inside is 

 blueish. 



It is found abundantly in the Thames, near the Red 

 House, and in the neighbourhood of Oxford. 



2. CYCLAS cornea. Shell subglobular, thin, semi- 

 transparent, striolate, with mostly a single groove 

 and a yellowish marginal zone. 



Cyclas cornea. Turton, Dith. p. 248. t. II. f. 14. 

 Cyclas rivalis. Drap. 129. 1. 10. f. 4, 5. 

 Tellina cornea. Linn. Gmel. 

 Cardium corneum. Montagu, p. 86. 



About half the size of the former, but much more 

 turgid, thinner and more transparent, one of the 

 sides being very slightly produced : it is also most 

 commonly marked with a single deep groove, and 

 bordered more or less with yellow : colour pale 

 yellow. 



In most stagnant ditches and water-courses. 



