74 
1003 Planorbis anitensis Cp. 
“Shell (when held mouth downward) with the right side con- 
cavo-convex, the left flat (or slightly concave), the left margin 
forming a sharp carina expanded beyond the edge of shell, which 
is marked by a compressed line. Whorls 5, visible on both sides, 
uniformly flat on the left side, forming a concave umbilicus on 
the right, where their surface is founded. Mouth triangular, the 
right lip arched, the left nearly flat, the extremities joined to 
outer angle and to obtuse margin of umbilical cavity. Umbilicus 
half as wide as the shell; flat side of mouth one-fourth of diam- 
eter; greatest breadth (at mouth) over one-fifth of same; greater 
diameter 0.26, least 0.03 inch.’’—Cooper, Cal ac pr 2d ser, 3:341. 
Type locality: Laguna at Santa Anita, Baja California, at an 
elevation of 100 feet, and 10 miles from San Jose del Cabo. 
1004 Planorbis deflectus Say. 
Great Slave lake to Virginia, Nebraska, and Montana. 
1005 Planorbis exacutus Say. 
Maine to Virginia, west to Kansas, Montana, and Vancouver 
Island. 
1006 Planorbis gracilentus Gould. 
Colorado desert, California ?—-Texas—Mexico. 
1007 Planorbis hornii Tryan. ~ 
Shell of three convex volutions; aperture almost orbicular, not 
oblique, nor extending above or below the plane of the whorls; 
labrum slightly reflected, thickened within, its ends converging so 
as nearly to connect on the parietal wall; lines of growth fine and 
close. Color light horn. Diameter 21, height 7 mm. 
Living: Fort Simpson, British America (George H. Horn). 
Grant’s lake, California (W. M. Gabb). 
1008 Planorbis opercularis Gould. 
Shell dextral, much depressed, lenticular, with a prominent 
blunted keel at compressed line; tip sunken; beneath the periph- 
ery defined by a marginal, umbilicated for about one-third the 
breadth of the base, showing 3 volutions, convex, surface rather 
rude and indented, marked with irregular, coarse, much arcuated 
lines of growth, and here and there a few obscure, raised revolv- 
ing tines; color dark chestnut brown, a little clouded; whorls 
above 4, slightly convex; suture well defined, impressed; aper- 
ture transversely subrhombic, lip above slightly acute-angled, be- 
neath arched, lips embracing % of that part of the whorl which is 
beneath the carina. Diameter 6, height 1.5 mm. 
Living: Common in the waters of California. Vancouver isl. 
1009 Planorbis peninsularis Cp. 
“Shell with both sides concave, the right with whorls rounded, 
their edge forming an obtuse margin, and the outer one partly 
enclosing the others so that it forms two-thirds the greater diam- 
eter of the shell. Whorls 5, visible on both sides, the rounded (or 
right) surface showing less of them than the other. Left (or 
umbilical?) surface nearly flat, deeply concave near middle, the 
umbilicus being over one-third of diameter. Mouth trapezoidal, 
very oblique, its lips curved, the right extremity attached near 
the concave spire, the left to the obtuse periphery of shell. Mouth 
one-third longer than wide; its breadth over one-third that of 
shell. Greater diameter 0.16, least 0.05 inch. Color brown, sur- 
face smooth.’’—Cooper, Cal. ac pr 2d ser, 3:342. 
Type locality: —‘‘With P. anitensis, in same laguna.’’ 
1010 Planorbis subcrenatus Cpr. 
Shell tumid, very thin, horn-colored; whorls 6, rounded, su- 
tures impressed; with sharp radiating, somewhat crowded and 
occasionally minutely crenulated ridges; aperture rounded, pari- 
