PISIDIUM. 265 



Monog. 13..t.20. f. 1. 3. ; Forbes and Hanley, B. M. ii. 120. 

 t. 36. f. 1. Cyclas obtusalis. Lam. Hist. v. 559. Pera 

 gibba. Leach, MSS. Brit. Mm., Syn. Moll. 292. ; Dupuy, 

 Moll Franc. 690. t. 31. f. 4. P. fontinale obtusale. Held, 

 Isis, 1837,306. P. (Cyclas) fontinalis, var. obtusalis. Dupuy. 

 Moll. Gers, 89. 



Young, the yellow zone broader. 



Var. 1., shell ovate, trigonal, very ventricose, blackish or 

 ochraceous ; the edge very blunt : Cyclas obtusalis. Nilson, 

 101. Cyclas obtusale ft. Jenyns, Monog. 13. 



Inhab. small splashy pools and other stagnant 

 waters. 



Animal white ; siphons short, obconic ; foot very 

 extensile. 



Mr. Jenyns observes : " It is by far the most active 

 and lively species that I am acquainted with, being 

 always in motion, and residing less at the bottom than 

 the rest of the family." 



121. 2. PISIDIUM nitidum. Shining Pera. Shell 

 orbiculate, oval, very shining, finely striated ; 

 umbones rather blunt, with a few deeper 

 striae; cardinal and lateral teeth moderate, 

 thin. (t. 12. f. 50.) 



Pisidium nitidum. Jenyns, Monog. 16. t. 20. f. 7, 8. ; Forbes 

 and Hanley, B. M. ii. 126. t. 37. f. 14. P. incertum. 

 Norm. Cyd. 6. Cyclas nitida. Hanley, Sp. Shell, i. 90., 

 Supp. t. 14. f. 46. 



Inhab. clear water, Cambridgeshire, Battersea 

 Fields. (Gray.} 



Animal white ; siphon short, funnel-shaped, with 

 a spreading mouth, and a more or less plaited cre- 

 nated edge. 



This shell may easily be distinguished by the 

 deeper grooves on the umbo, which are more easily 

 seen in the living specimens. 



