THE NATURAL HISTORY SURVEY. 403 
valve moderately curved, its posterior end thicker; the infe- 
rior in the left valve curved, the superior little so or almost 
straight; lateral teeth very short, very abrupt, pointed, thin, lit- 
tle projecting into the cavity of the mussel; ligament small. 
(Sterki.) 
Lgth., 4.00; height, 3.60; breadth, 2.80 mill. 
aes ho (0 ee mi 2.80; as 2.40 “ orless(deepwaterform). Sterki. 
Animal: Not examined. 
Distribution: ‘Pine Lake, 5-11 meters; Lake Michigan, 
off New York Point, 24 meters; also taken from the stomachs 
of whitefish of Lake Michigan; various parts of Michigan and 
Minnesota” (Sterki); Lake Michigan near Chicago (Baker); 
Huntley, Ill. (Ferriss). ‘Sterki says of these specimens that 
they are smaller and much less full than the typical examples 
from Lake Michigan” (in letter). 
Geological distribution: Pleistocene. 
Habitat: Collected at considerable depths in the larger 
lakes, and in numerous small lakes and rivers. 
Remarks: ‘This is one of our most characteristic Pisidia, 
distinguished, besides its surface features, color, and the con- 
figuration of the hinge, by its oblique shape and the much 
larger anterior part. This character it has in common with 
Pis. virginicum Gmel. and walkeri; the former of these is out of 
the question; the latter species is much more angular and the 
surface dull, from microscopic lamellz, but even.” 
“Pts. scutellatum is somewhat variable; the largest speci- 
mens seen, from Orchard Lake, Mich., are 4.5 mill. long. Those 
from deep water are the smallest and most inflated, and their 
beaks are commonly more prominent; some of them have 
crowded striz of growth.” (Sterki.) 
The specimens from Chicago were found in drift along 
the lake shore at Miller’s, Ind., and were probably washed up 
from deep water. 
158. Pisidium punctatum Sterki, pl. xxxi, figs. 17, 18, 22. 
Pisidium punctatum STERKI, The Nautilus, Vol. VIII, No. 9, p. 99, Jan. 
1895. 
Shell; ‘Minute, inequipartite, high, oblique, strongly ven- 
tricose, almost globular, regularly and sharply striated, micro- 
scopically rugulose, whitish; anterior part moderately long, 
the edge above oblique, almost straight, end slightly angled, 
rather inferior; anterior part short, truncate, slightly angular 
