286 CONCHIFERA. 



viii. 60.; Dillwyn, D. Cat. i. 105.; Turt. Diet. 



168. 

 Tellina rivalis, Maton, Linn. Trans, ii. 44. t. 13. 



f. 37, 38. ; Don. B. Z. t. 64. f. 2. 

 Cardium amnicum, Montag. T. B. 86. 

 Cyclas palustris. Drap. 131. t. 10. f. 15, 16. 



obliqua. Lam. Hist. v. 559. ; Nilson, 99. 



Pisidium obliquum. Pfeiffer, 124. t. 5. f. 19, 20. 

 Cyclas amnica. Turt. Biv. 250. t. 11. f. 25., 



Man. ed. 1. 15. f. 5. ; Fleming, B. A. 453. 

 Pisidium amnicum. Jenyns, Mon. 21. t. 21. f. 2. 

 Young shell rather compressed; umbones scarcely 



prominent. 



Var. 1. Shell with very deep grooves. 

 Pera fluviatilis. Leach,, MSS. in Brit. Mus. 

 Pisidium amnicum /3. Jenyns, Mon. 22. 

 Var. 2. Shell nearly smooth, with slighter striae. 

 Pera Henslowiana. Leach, MSS. Brit. Mus. 

 Pisidium amnicum 7. Jenyns, Mon. 22. 



Inhab. rivers and gently running streams, residing 

 wholly at the bottom, and being partly buried in the 

 mud. 



Animal white, siphon rather variable. 



121. 7. PISIDIUM cinereum. Shell greyish or cinere- 

 ous, rather compressed, oval, finely striated, 

 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. 

 Pisidium cinereum. Alder, Cat. Supp. 4. 



