THE LIFE OF GLACIAL LAKE CHICAGO 95 



the Chicago outlet at this time, this region being for the most part a quiet bay. 

 Thirteen species of mollusks, an insect or two, and a few bones of fish were 

 obtained from these deposits. These are noted below. 



Mollusks 

 Anodonta species Planorbis exacuous 



Valvata tricarinata " parvus 



Amnicola limosa Ancylus parallelus 



" lustrica Galba palustris 



Physa warreniana " reflexa 



Planorbis campamdatus Lymnaea stagnalis appressa ' 



" antrosus 



Insects 

 Donacia proxima Coleoptera, punctostriate elytron 



Fish 

 Fragments and small bones. 



The insec.s were referred to Prof H. F. Wickham, Iowa State University, 

 Iowa City, Iowa, who writes as follows concerning the Donacia: 

 "The specimen is a fragment showing the base, part of the humeral and sutural 

 regions and a portion of the disk of the left elytron, with colors well preserved, 

 the wing-cover being blue-black over the disk and bright metallic green about 

 the humerus. The sculpture is remarkably clearly exhibited, agreeing even 

 in minute detail with recent specimens of D. proxima in the size, shape, arrange- 

 ment and dist'nctness o ' th? punctures, the lack of interstitial rugosities on 

 the inner half of the elytral disk and the presence of fine transverse wrinkles 

 in the humeral region. Donacia proxima is one of the most characteristically 

 colored and sculptured of all the North American forms and is pretty easily 

 recognized by those features alone. There is no reason to doubt that the fossil 

 is specifically the same as the modern specimens with which it has been 

 compared. 



" Donacia proxima is now classified as a race or variety of D. cincticornis 

 Newm. It occurs in Canada from Vancouver Island to Newfoundland as well 

 as in California, Oregon, Idaho, Iowa, Wisconsin, Indiana Pennsylvania New 

 York, New Hampshire and Massachusetts, on the leaves of water plants. No 

 special conclusions as to climate can be drawn from its presence as a fossil. 



"In this connection, it is interesting to note that the genus is well repre- 

 sented in fossil condition, about thirty species being noticed or described from 

 Tertiary and Pleistocene beds. The habits of the insects and their hard integu- 

 ments combine to render their preservation more than usually likely. " 



I. THE PRESENT GREAT LAKES 



Following the Nipissing stage the lake waters were gradually lowered by 

 the cutting down of the St. Clair outlet. This gradual lowering of the lake 



