PISIDIUM. 73 



This species, allied only to P. ventricosum, is remarkable for 

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



Fig. 82. 



p. rotundatum. 



15. Pisidium occidentale, Newcomb. — P. testa rotundato- 

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

 matis vie prominentibus ; striae minutissimae. 



Long. 4 ; Lat. 3| mill. 



Hab. 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. Newcomb says is allied 

 to P. variahile. 



Fossil Species. 



16. Pisidium contorttiiu, Pkime. — Shell elongated, subrhom- 



boidal, inequilateral, somewhat compressed ; anterior side 



produced, angular at end ; posterior side short, subabrupt ; ^ig* ^3. 



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. 

 Eab. 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. 



