THE CHICAGO ACADEMY OF SCIENCES. 



Minnesota: Mississippi River, Stearns Co. (Walker). 



New York: Erie Canal. Lock 65, Rochester; Round Pond, near Charlotte; 

 Sea Breeze, Irondequoit Bay; Monroe Count}- (Baker). 



Tennessee: Tennessee (Lea; Troost). 



West Virginia: White Sulphur Springs, Greenbrier Count}- (Lea; N'ick- 

 lin). 



Wisconsin: Milwaukee. Milwaukee Co. (Smith. Inst.). 



Geological Range : Pleistocene. 



MARL EEDS. 



Michigan: Arnolds Lake, Washtenaw County (Walker). 



Ecology : In bayous, small ponds, lakes and streams, and the 

 protected shores of rivers, on mud flats and in situations similar to 

 those in which Galba humilis modicetta lives. In Illinois the species 

 is generally found in ditches and on the margins of small lakes. In 

 New York it is found in swampy places and on the protected shores 

 of lakes and bays. 



Mr. Van Hyning, of Des Moines, Iowa, has recorded an inter- 

 esting case of protective resemblance. In a pond below Chesterfield, 

 near Des Moines. Iowa, rather small, narrow specimens of cxigua 

 occur. Those living on a sandy bottom have whitish, horn-colored 

 shells, while those living on a muddy bottom or in moss are almost, 

 and in some cases quite, jet black. 



Remarks : This small variety appears quite separable from 

 obrussa. The spire is usually long and the whorls are flat-sided and 

 compressed, giving their upper parts a strongly shouldered appearance; 

 the aperture is more regularly ovate than in obrussa, and the inner 

 lip is peculiarly flattened near the umbilical region, giving rise to a 

 pseudo-plait. The most noteworthy feature is the very deep suture, 

 which is almost channeled in many specimens, causing the whorls to 

 be turban-shaped. This feature is present in the majority of the indi- 

 viduals examined. This race will probably be found in many collec- 

 tions under the names of desidiosa or humilis. Specimens from Des 

 Moines are striped in zebra fashion. 



This neat little variety is usually easily separated from obrussa. 

 At Des Moines, Iowa, the variety' is connected with obrussa by inter- 

 mediate forms, but in most of the lots examined the variety is very 

 constant. Exigua is liable to be confounded with Galba humilis rustica, 

 but in that race the spire is acutely conical, the whorls regularly in- 

 crease, the body whorl is not compressed in the middle, and the 

 aperture is roundly ovate, while in cxigua the spire is broadly turreted, 

 the whorls are disproportionate in size and the body whorl is very 

 cylindrical. (See the figures on plate XXXII.) 



