104 



GEOLOGY OF LA SALLE COUNTY. 



of October, Limnoea stag-nalis, L., being- the last I 

 have found at the surface, and this on the first of 

 November. 



SUBFAMILY LIMN^IB^. 



Shell spiral, spire more or less acute, last whirl 

 large, aperture larg^e. 



GENUS LIMN^A, LaM — SUBGENUS LYMNOPHYSA, 



FITZ. 



Limn^a reflexa. Say. — Shell, dextral, elongated, 

 volutions six, which are very oblique and wrinkled, 

 spire acute and long-, body whirl dilated, aperture 

 rather narrow% shell reflected from the middle, leng-th 

 one and one-fourth inches. Illinois river. 



Limna^a pallida, Adams. — Shell thin, whirls five, 

 suture marked, horn color, body whirl not much 

 enlarg-ed, fold upon the columella not larg-e. leng-th 

 one-half inch. Ivoc. Fox and Illinois rivers. 



Ivimnaea humilis. Say. — Shell small, horn color, 

 length 8 mill. Found in swales near Illinois river. 



Ivimnaea desidiosa. Say. — Shell oblong-, spire long- 

 as the aperture, whirls five, of a yellowish horn color, 

 length, 10 mill. Found in same locality as the preced- 

 ing species. 



Ivimnsa caperata, Say. — Shell conic, whirls five, 

 suture distinct, apex acute, whirls wrinkled, and with 

 light-colored revolving lines on the young shell, aper- 

 ture dilated somewhat, labium without much fold, 

 color yellowish horn, with frequently bands of white, 

 aperture reddish within, length 14 mill. 



GENUS PHYSA, DRAP. 



The Physas are the most active and hardy of all 

 the aquatic univalves. They move rapidly through 

 the water shell downwards. They inhabit muddy 



