NATURAL SCIENCES OF PHILADELPHIA. 103 



fiere, but at a more recent date. No shells of this species have 

 been found here earlier than 1855, since which time they have 

 gradually increased in size and numbers. The largest shell yet 

 found is 1.83 inches long. It is in the collection of Mr. Charles 

 M. Wheatley, of Phoenixville, Pa. 



Physa heterostropha, Say. 



Common in rivers and streams; also in stagnant water. Some 

 of the varieties simulate the forms of gyrina, ancillaria, and inte- 

 gra, but I do not think, from all I have seen, that either of those 

 species can be entered here. 



Physa hypnorum, Drap. 



A small variety. Not common. 



Planorbis armigerus, Say. 



Sometimes very abundant in stagnant water. It is not constant 

 in the stations where found. 



Planorbis bicarinatus, Say. 



Erie Canal, Mohawk River, Schuyler's Lake, Little Lakes, and 

 Smith's Pond. Shells found in Smith's Pond are very white, like 

 ivory. Those found in Little Lakes are small and pale, but not so 

 white as those of Smith's Pond. 



Planorbis campanulatus, Say. 



Lakes and ponds. The few found in Smith's Pond are white, 

 like bicarinatus in the same pond. 



Planorbis deflectus, Say. 



Lakes. Not abundant. 

 Planorbis exacutus, Say. 



Lakes. Not abundant. 

 Planorbis parvus, Say. 



Stagnant water. Sometimes (rarely) abundant. 

 Planorbis trivolvis, Say. 



Canal, rivers, lakes, and stagnant water. 

 Planorbis hirsutus, Say. 



Schuyler's Lake. Rare. 

 Pisidium abditum, Haldeman. 



I think P. variabiles Prime, may be included under this species 

 as a synonym. The shells occur in a great variety of stations. 



1872.] 



