PISIDIUM. 



269 



and with two or three deep sulcations, forming 

 darker zones across the shell ; margin of the 

 valves meeting at a rather acute angle ; umbones 

 obtuse, and not much produced, sometimes 

 slightly capped, as in C. calyculata; cardinal 

 teeth rather prominent; lateral moderate and 

 thin. (t. 12. f. 152.) 



Cyclas cinerea. Hanley, Recent Shells, i. 90. t. 14. f. 44. 

 Pisidium cinereum. Alder, Cat. Supp. 4. ; Forbes and Han- 

 ley, B. M. ii. 125. t. 36. f. 2. Cardium cajertanum. Poli, 

 Sicil. i. 65. t. 16. f. 1. Pisidium cajertanum. Bourg. Voy. 

 Mer. Mort. 80.; Moq. Tand. Moll. Franc, ii. 584. t. 52. 

 f. 16 32. Pisidium australe. Philip. SiciL \. 39. Cyclas 

 lenticulare. Norm. Cycl. 8. t. 8. f. 7, 8. P. lenticulare, 

 Dup. H. M. 681. t. 30. f. 2. P. tetragonum. Norm. 

 Cycl. 5. P. thermale, P. normandianum, P. Iratianum, 

 P. Gassierianum, and P. calyculatum. Dupuy, Cat. P. 

 limosum. Gass. Moll. Agen. 206. t. 2. f. 10, 11. 



Distorted : P. sinuatum. Bourg. Jour. Conch. 1851, 421., 

 1852, 49. t. 1. f. 6 10. 



Var., more ventricose, and produced at the umbones. 



Inhab. ponds, North of England. 



Animal white ; siphonal tube very short, broad, 

 and flat, truncated at the end, and seldom protruded 

 much beyond the edge of the shell. 



This species may generally be readily distinguished 

 from others of the genus by its more compressed and 

 oval form, and its cinereous colour. It is the largest 

 of the minute species. (Alder.) 



Length 2-10ths, height 7-40ths, thickness 5-40ths 

 of an inch. 



The genus Cyrena is now no longer found alive 

 in this country, but it must have lived here at no very 

 great period of time (geologically considered), for it 

 is found an abundant fossil at Grays, in company 



