The Deep Water Crustacea of Green Lake. 213 



ages somewhat smaller than the type. These differences are so minute 

 that I consider them only varietal, although they are constant in the 

 specimens I have examined. 



Diaptomus minutus has been found, hitherto, only in Greenland and 

 Newfoundland, although it seems probable that it is widely distributed 

 over the northern part of North America. 



Pontoporeia Hoyi Smith, has been found, hitherto, only in Lake Super- 

 ior and Lake Michigan. A species almost identical with it, pontoporeia 

 affinis Kroyer, occurs in the abyssal fauna of the Scandinavian lakes. 



Mysis relicta Loven, was first found in the Scandinavian lakes. It is 

 so closely allied to mysis ocidata Kroyer, a marine form found off the 

 coast of Labrador and Greenland, as to be considered only a variety of 

 that species. It was found in Lake Michigan by Dr. Hoy, receiving the 

 name of mysis diluvianus from Prof. Stimpson. Later, Prof. S. I. Smith 

 collected specimens in Lake Superior. I have not had an opportunity 

 to compare my specimens with those from the Great Lakes, or with the 

 original description of the Scandinavian form, but I have [little doubt 

 that they are identical with them. 



When we compare the deep water Crustacea of Green Lake with those 

 of Lake Michigan and Lake Superior, as shown in the lists published 

 by Prof. Smith and Prof. Forbes, we find a striking similarity. That 

 this should be true of the pelagic fauna is not strange, for it is easy to 

 explain the migration of such forms from one body of water to another 

 through the agency of water fowl. 



The presence of pontoporeia Hoyi, and mysis relicta however, is not 

 so easily explained. They are abyssal forms, found only in deep water, 

 and never coming to the surface. Their presence in the Scandinavian 

 lakes is explained by supposing that the bodies of water, in which they 

 are found, were formerly connected with the sea, and that, when the ac- 

 cess of salt water was cut off, the change to fresh water was so gradual 

 that the animals accustomed themselves to their new conditions of exis- 

 tence. They belong to the " fauna relegata " or " relickten-fauna " of 

 the Germans. This explanation does not seem to apply to Green Lake. 

 The lake is of glacial origin, a dam of drift at the western end prevent- 

 ing its waters from flowing into lake Puckaway. The outlet of the lake 

 is a small stream flowing through the village of Dartford, and emptying 

 into the Fox River. So far as I know, there is no geological evidence 

 whatever of any connection of Green Lake with either the Mississippi 

 Basin or the Great Lakes, by which these deep water animals could have 

 migrated to their present location. 



The problem is one for which I can at present offer no solution. 



