PISIDIUM. 
265 
Monog, 13. t. 20. f. 1. 3. ; Forhes and Hanley^ B. M. ii. 120, 
t. 36. f. 1. — Cyclas obtusalis. Lam, v. 559. Pera 
gibba. Leach,, MSS, Brit, Mus,,, Syn, Moll, 292. ; Bupuy,, 
Moll, Franc, 690. t. 31. f. 4. — P. fontinale obtusale. Helk,, 
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 jS. 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, Cycl, 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. 
