73 



990 Physa gyrina Say. 



Northern United States and Territories — Oregon, Nevada; 

 Strawberry Creek, Berkeley, Cal. (R. E. C. Stearns). 



991 Physa heterostropha Say. 



Northern half of United States and Canada — Oregon? 



992 Physa humerosa Gld. 



Shell subrhomboidal, solid, smooth and white; spire acute; 

 whorls 5, tabulated; aperture one-half to two-thirds length of 

 shell, rounded posteriorly; labrum expanded; columella scarcely 

 plicate, callum hardly perforate. Length 15, diameter 9 mm. 



Living: Colorado river; Pyramid lake, Nevada; Pecos river, 

 Texas. 



Quaternary: Near Carson, Nev. Very abundant on the Col- 

 orado desert in a "semi-silicified" condition. 



Virtually only a distorted form of P. heterostropha; evidently 

 the same form occurs living in the Los Palmas springs, Colorado 

 desert. 



993 Physa hypnoruni Linne. 



Circumboreal — south to New England, Ohio river, and Wash- 

 ingtonia. 



994 Physa Lordi Baird. 



Shell thin, corneous, tumid, gibbous, aperture large, outer lip 

 acute; external surface very minutely decussated; whorls 6, first 

 2 minute, tinged with black, the last swollen, 4 times the size of 

 the others. Length 19-25, diameter 12-18 mm. 



Living: Lake Osoyoos, British Columbia. Washington. Hum- 

 boldt lake. Nevada. 



995 Physa malleata Tryon. 



Montana and Northern California to Nevada. 



996 Physa triticea Lea. 



Oregon and Northern California. 



997 Pilidium fulvum Muller. 



Circumboreal? — Finmark to Ireland — Alaska — Asia. 



998 Placiphorella latior Carpenter. 

 Monterey, Cal. 



999 Placiphorella imporcata Carpenter. 



Vancouver Island to Santa Barbara Islands, California. 



Dall, U. S. na mu pr 1:306 (1878). 



Mopalia imporcata Cpr. Phila ac pr 1865:59. 



Puget Sound; Santa Barbara Islands, Cal. 



1000 Placiphorella sinuata Carpenter. 

 Straits of Fuca to Monterey, California. 

 Dall, U. S. na mu pr 1:306 (1878). 

 Mopalia sinuata Cpr. Phila ac pr 1865:59. 

 Puget Sound; San Francisco bay, California. 



1001 Placiphorella velata Carpenter. 

 Southern California. Vancouver Isl. 



1002 Planorbis amnion Gould. 



Shell large, discoid, subconic, delicately striate; left side 

 broadly and deeply concave, showing 4 obtusely carinated whorls; 

 right side concave, showing 2% rounded whorls; aperture ovate 

 triangular, sometimes quite expanded on each side; axis, five- 

 eighths to one; diameter % to V 2 inch. 



Living, Klamath lake, Oregon, Honey lake, Lassen county, 

 Cal. Nevada, Colorado river. 



Quaternary: Clenega Grande, Colorado desert. — T. H. Webb; 

 W. P. Blake, Lahontan basin, Lassen county, California. 



