VOL. IIl.] Lower Californian Shells. 23 
others have, however, traced the same species so common as fossils 
in the desert, along New River, and they no doubt exist, sub-fossil 
if not all living, to the mouth of the Colorado River, or to tide- 
water, fear lat. 32°. ; 
38. AMNICOLA LONGINQUA Gould, 1855. Living at Lake 
Point, Utah, Hemphill. Quaternary, Nevada to Colorado Desert. 
39. ANODONTA (NUTTALIANA) CALIFORNIENSIS Lea, 1852. 
Living, British Columbia to Arizona, Colorado River, ¥ L. Le- 
conte; etc. 
40. GNATHODON MENDICUS Gould, 1851. Living, Colorado 
estuary, Dr. /. L. Leconte, to Mazatlan, Mexico, in brackish water, 
Reigen. 
41. HELISOMA AMMON Gould, 1855. Klamath Lake, Oregon, 
to Colorado Desert, (and river, 7, G. Cooper). 
42. PHYSA HUMEROSA Gould, 1855. Pyramid Lake, Nevada, 
to Colorado River, and Texas, Blake, Wedd, etc. 
43. PLANORBIS GRACILENTUS Gould, 1855. Colorado Desert, 
Dr. T. H. Webb. P. leibmanni Dunker, 1844,? from Vera Cruz, 
Mexico, is supposed by Binney to be the same species, and identified 
from Texas also. No confirmation of the desert locality recently. 
44. TRYONIA CLATHRATA Stimpson, 1865. Colorado Desert, 
fossil only? W. P. Blake. Lately reported as living in Utah, 
(Stearns.) 
45. 7. Ex1GUA Conrad, 1855. Living, southern Utah (to Dos 
Palmas Springs, lat. 33° 30’, Colorado Desert, Orcutt). 
All the above except 40 and 43, are found in vast nnmbers around 
the shores of the dry lake constituting the desert, as fossils, Quater- 
nary, or later. These are chiefly of more northern species than 
most of the peninsula shells, Nos. 4o? and 43 only, being now 
limited to the south of the boundary, and are all aquatic. Only 41, 
42, 43 are pulmonate, the others being of orders not represented on 
the peninsula. 
The portion of the desert south of the boundary is a triangular 
tract about 70 miles along the boundary, and 130 along the 115th 
meridian (which are nearly at right angles), the third side at foot of 
the mountains being about 150 miles long, and ending near lat. 
31°, thus embracing about 4,550 square miles. A large part of this 
