P1SID1UM. 



This species, allied only to P. ventricosu-m, is remarkable for 

 the fulness of the beaks, which are not raised in proportion. . 



Fig. 82. 



P. rotundatum. 



15. Pisidium occidentale, NEWOOMB. P. testa rotundato- 

 ovata, obliqua, inequilatera, hyalina vel fusco-cornea ; natibus approxi- 

 matis vie prominentibus ; strife minutissimse. 



Long. 4 ; Lat. 3| mill. 



Hob. North America, at San Francisco (Ocean House), California. (Cabi 

 net of Newcomb.) 



Pisidium occidentale, NEWCOMB, Proc. Calif. Acad. Nat. Sci. II, 1863, 94. 



I have not seen this species, which Dr. Newcoinb says is allied 

 to P. variabile. 



FOSSIL SPECIES. 



16. Pisidium contortum, PRIME. Shell elongated, subrhom- 

 boidal, inequilateral, somewhat compressed ; anterior side 

 produced, angular at end ; posterior side short, subabrupt ; Fig. 83. 

 hinge and basal margins nearly straight ; beaks terminal, 



raised above the outline of the valves ; striae light ; hinge 



comparatively strong ; cardinal teeth distinct ; lateral teeth 



, P. contortum. 



elongated. 



Long. 0.13 ; Lat. 0.07 ; Diam. 0.05 inches. 



Halt. North America, at Pittsfield, Massachusetts. Post Pleiocene for 

 mation. (Cabinets of Smithsonian Institution, and Prime.) 



Pisidium contortum, PRIME, Ann. N. Y. Lye. VI, 1853, 65, pi. i, f. 2. 



This species, which occurs rarely, was discovered, by Dr. Shurt- 

 leff, in company with P. ventricosum. 



