INDUSTRIAL PROGRESS DURING THE YEAR 1875. clxxxvii 



ohionis, a shrimp used for food in Indiana, and another 

 shrimp Palcemonetes exilipes of Stimpson which occurs in 

 Lake Erie as well as South Carolina and the fresh -water 

 streams of Florida. The most remarkable shrimp-like form, 

 however, is the .Mysis relicta, first described by Loven, from 

 the inland lakes of Sweden. It occurs at various depths in 

 Lakes Superior and Michigan, where it forms a large part of 

 the food of the whitefish. 



This Mysis is so closely allied to the Mysis oculata of 

 the northern and arctic seas, being regarded by some as a 

 simple variety, that its occurrence in these lakes so far from 

 the sea is, as Smith states, a fact of peculiar interest, which 

 goes far toward proving the marine origin of a part of the 

 fauna of our great lakes. Dr. Stimpson believed that the 

 great lakes had in recent (Quaternary) times been isolated 

 from the sea by a rise of land. Very probably, at the time 

 when the sea had access to these basins, the communication 

 was somewhat narrow and deep, and the influx of fresh 

 water from the surrounding country was sufficient to occupy 

 entirely the upper stratum, while the heavier sea-water re- 

 mained at the bottom. 



After the basin had become separated from the ocean by 

 the rise of the land, the bottom water must have become 

 fresh by diffusion very slowly to allow of the gradual adap- 

 tation of the crustaceans to the change of element." Pro- 

 fessor Smith adds that at the time Lake Ontario was a part 

 of the great St. Law T rence valley sea, there was, very likely, 

 no insuperable barrier in the Niagara River to the upw T ard 

 migration of active swimming animals like Mysis, and some 

 of the inhabitants of the upper lakes may have reached their 

 present homes by this route during the northern movement 

 of the fauna at the close of the Quaternary epoch. " On the 

 other hand, Jfysis relicta, although originally derived from 

 the strictly marine species M. oculata, may have existed 

 long enough to have had the same history as some of the 

 strictly fresh-water species, known to be common to Northern 

 America and Northern Europe, since it has much the same 

 geographical distribution." Other Crustacea are mentioned 

 in Professor Smith's " Sketch of the Invertebrate Fauna of 

 Lake Superior," in the same report. 



The habits of the blind crawfish of the Mammoth Cave have 



