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 
Pplicate, 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 hypnorum 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 ammon 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 % 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. 
