THE NAUTILUS. 57 



any of the pre-glacial streams of that region, of the pre-glacial fauna, 

 and not from a post-glacial invasion from the south, it would seem 

 a necessary result that the Unione fauna of the entire region should 

 be to-day of the same general character, and that the peculiarities of 

 the present Lake Erie fauna should be also characteristic of the 

 same species as found in the interior waters of the State. But that 

 is not the fact. The differentiation that has occurred is entirely in 

 the race which is found in the colder waters of the Great Lakes. 

 In the warmer waters of the interior of the State, the species attain 

 the same size, the same luxuriance of growth and the same color 

 that they do at the present time in the Mississippi and Ohio valleys. 

 In other words, the interior waters of the Lower Peninsula of 

 Michigan are inhabited by the typical forms of these species just as 

 clearly and as certainly as the examples found in the Great Lakes 

 are peculiarly modified into what is known as the Great Lake forms. 

 Thus, for example, the Great Lake form of the species known as 

 Lampsilis recta is depauperate, and standing by itself, would seem 

 to be specifically different from the typical form. It was described 

 as a distinct species under the name of sageri by Conrad. But in 

 the Rouge River, less than ten miles from Detroit River, and in the 

 Clinton River, at Mt. Clemens, at no greater distance from Lake 

 St. Clair, examples of this species are typical in every respect, and 

 are as large and heavy as the average specimens from the Ohio and 

 Mississippi valleys. The same is true of nearly every species now 

 represented in the peculiar fauna of the Great Lakes. That being 

 the case, it is obvious that either one of two things must be true. 

 There has been no natural connection between the St. Lawrence 

 region and the Ohio Valley since the Maumee outlet of the post- 

 glacial Lake Erie was cut off by the retreat of the ice and the 

 establishment of another outlet at a lower level. If the present 

 Lake Erie fauna was the survival of the pre-glacial fauna of that 

 region, then the interior of the State must have been populated by 

 migration upstream from the relict fauna of the Great Lakes, 

 and it hardly seems possible if that were true, that the subsequent 

 modifications of these species from the Great Lake form consequent 

 upon their introduction to a different environment, warmer water ) 

 and more abundant food, should have been directly back to and 

 exactly coincident with the typical form as found in the regions 

 south of the glaciated area. On the other hand, if that is not so, the 



