268 
PISIBIABiE. 
then gradually rise to the umbo as the shell in- 
creases in size by the addition of new laminse of 
shelly matter to its edge. 
The apex of the umbo is sometimes deficient. 
125. 6. PisiDiUM Shell ovate, ventricose, 
deeply sulcately striated; umbones rather 
blunt, simple ; cardinal teeth prominent, well 
developed, diverging like a V ; lateral teeth 
moderate, thin. (t. 1. f. 5.) 
Tellina amnica. Muller^ ii. 205. ; Linn. Trans, viii. 60. ; 
Dilhvyn., D. Cat. i. 105. ; Turt. Diet. 168. — Tellina striata. 
Schroet. Flussconch. — Tellina rivalis. Maton., Linn. 
Trans, ii. 44. t. 13. f. 37, 38.; Don. B. Z. t. 64. f. 2. — 
Cordula amnica. Leach^ Syn. Moll. 293. — Cardium amni- 
cum. Montag. T. B. 86. — Cyclas palustris. Dray. 131. 
t. 10. f. 15, 16. — Cyclas obliqua. Lam. Hist. v. 559. ; 
Nilson, 99. — Pisidium obliquum. Pfeiffer.^ 124. t. 5. f. 19, 
20. — Cyclas amnica. Fleming, B. A. 453. ; Turt. Biv. 250. 
t. 11. f. 25., Man. ed. 1. 15. f. 5. — Pisidium amnicum. 
Jenyns, Mon. 21. t. 21. f. 2.; Moq. Tand. M. F. ii. 533. 
t. 52. f. 11 — 15.; Forhes and Hanley, B. M. ii. 133. t. 37® 
f. 8, 9., t. O. f. 8.— Cyclas PfeifFeri. Ziegl. — Pisidium inter- 
medium. Gass. Pisid. Aquit. 11. t. 1. f. 4. — P. Gratelou- 
peaiium. Norm. Cycl. 4. — P. inflatum. Megerle. 
Young shell rather compressed ; umbones scarcely prominent. ' 
Var. 1., shell with very deep grooves. Pera fluviatilis. Leach., 
MSS. in Brit. Mus., Syn. Moll. 292.~Pisidium amnicum /3. 
Jenyns, Mon. 22. 
Var. 2., shell nearly smooth, with slighter strise. Pera Hen- 
slowiana. Leach, MSS. Brit. Mus. - — Pisidium amnicum y. 
Jenyns, Mon. 22. 
Inhab. rivers and gently running streams, residing 
wholly at the bottom, and partly buried in the mud. 
Animal white ; siphon rather variable, obliquely 
truncated. 
126. 7. Pisidium Shell greyish or cine- 
reous, rather compressed, oval, finely striated. 
