130 THE CHICAGO ACADEMY OF SCIENCES. 
and is. variabile Pr.; from the former it is different by its 
being somewhat smaller, comparatively shorter and higher, the 
beaks being less full, the surface finer striated and more pol- 
ished; from the latter it is distinguished by its smaller size, the 
beaks being less full, the antero-superior margin less straight, 
and the angle at the anterior end being situated higher up; the 
shell is thinner and the hinge less strong, the coloration differ- 
ent. With all these differences appearing only gradual, our 
Pisidium is a good species beyond a doubt and will always be 
recognized.” (Sterki. ) 
Distribution: This species has been found thus far at the 
following localities: New Philadelphia, Ohio; Philadelphia, 
Pa.; Grand Rapids, Mich.; Clearwater River and Dallas Lake, 
Minn.; Joliet, Ill. 
Habitat; Found in company with /is. abditum and com- 
pressum.* 
*Besides the foregoing there are a number of forms of Sfheria and Pisidia now in the 
hands of Dr. V. Sterki, which he has not fully investigated. When these are determined, no 
doubt many new forms will be added to our fauna. 
