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. 



" 3.30; " 2.80; " 2.40 " or less (deep water form). 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, 111. (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 lamellae, but even." 



tf pis.scutellatwnis 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 striae 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, pi. 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 



