92 LIFE OF THE PLEISTOCENE 



part of Wilmette Bay must have been comparable to the southern portion of 

 Braddock's Bay, especially that part bordering the shores (see map Plate 

 XXXIX, and Plate XLIII). This habitat afforded an ideal home for shallow 

 water mollusks, as indicated by the subjoined list. 



Sphaerium stamineum Planorbis parvus 



emarginatum Segmcnlina armigera 



Musculium truncatum Galba caperata 

 Pisidium qffine " reflexa 



Physa gyrina Succinea retusa 

 Planorbis Iriiolvis " avara 



Cambarns blandingi acutus 



The crayfish is a pond or lake form, not a river form, and is the only repre- 

 sentative of the subgenus Cambarus living in this territory (vide Ortmann). 

 The remains of this crayfish were numerous, but always poorly preserved, 

 consisting of a broken carapace, several chelse, and fragmentary legs. This 

 crustacean lives among vegetation, in woodland swamps, shallow ponds and 

 pools, burrowing occasionally in the black muck soil. 



Dr. A. E. Ortmann, to whom specimens were submitted, remarks upon the 

 material as follows: "The specimen, of course is awfully poor; but as it hap- 

 pens, one very important character is seen: the corpulatory hooks of the 

 ischiopodites of the 3rd and 4th peraeopod of the left side, are distinctly seen. 

 Species with this character (subgenus Cambarus) are all southern, with the 

 exception of C. blandingi, and this excludes all other species found at the 

 present time in your region. After ascertaining this, and also ascertaining 

 that the specimen is, according to these hooks, a male of medium size in the 

 second form (impotent, not able to copulate), I compared it with specimens of 

 the living form, C. blandingi, of the same size and condition, and found com- 

 plete agreement. The fortunate circumstance that this is a male, and that it 

 shows the characteristic hooks of the ischiopodite is all-important, and I do 

 not hesitate at all, to assign it to the species as given above." 



b. Sag Outlet (Calumet-Sag Channel) 



In the Sag outlet a deposit of fine sand overlying the gravel deposit evi- 

 dently represents the deeper water of the Hammond stage. Eleven species of 

 mollusks have been noted from this stratum. 



Elliptio gibbosus Valvata Iricarinata 



Sphaerium acuminatum Physa Integra 



Pisidium virginicum Planorbis parvus 



Goniobasis livescens Galba obrussa 

 A nmicola limosa " palustris 



" lustrica 



