IN' THE WATERS OP THE LAKES. 5 



from two other localities in Ohio, from New York and from 

 Florida, but sparingly. The Actinocyclus niagarae, named 

 by Professor H. L. Smith, and described in the American Quar- 

 terly Microscopical Journal, October, 1878, was also sent to him 

 by Mr. Gaylord, and has not yet, so far as I can learn, been re- 

 ported from any other locality than Cleveland. The other spe- 

 cies of Amphiprora are marine, and those of Actinocyclus ma- 

 rine or fossil. 



Some other species of diatoms found in the lakes are so 

 modified in form as to be perceptibly different from the same 

 typical species found elsewhere. From these facts Prof. Smith, 

 above named, suggested the query whether salt or brackish 

 water might not be found at the bottom of the lakes; but from 

 the shallowness of Lake Erie that is improbable in this case, and 

 my own conclusion is that these forms of diatoms are survivors 

 of the ancient sea, which have, during the subsidence of the 

 former sea, survived the change through brackish to fresh water, 

 perhaps not modified in form during the change. As bearing 

 upon this view, many facts which have come under my observa- 

 tion may be cited. Some three or four years ago, after repeated 

 desultory examinations of the lake water, I began a systematic 

 course of taking filterings, and at first supposed that filterings 

 of each of the four seasons of the year would display the species 

 of the year; but during the second year of such observations I 

 became convinced that more frequent tests were needed, and 

 took filterings from twice to three times per month, and during 

 the year 1879 I saved a filtering of each week of the year, ex- 

 cept during two short absences. Examination of the filterings 

 when taken confirmed what had been deduced from former ob- 

 servations, that the forms of life in the lake water exhibit a well 

 marked periodicity, the limits of which I have not continued 

 the observation far enough to exactly define at present, but 

 which as far as the diatomacese are concerned, can be in general 

 terms stated thus: During that part of the year from about 

 the first or middle of February to about the first of May, the 

 variety of form is greater; from thence to about November 1 

 the abundance of the prevalent forms is greatest, and from No- 

 vember 1 to about February 1 the disappearance of warm weath- 

 er forms and appearance of the cold weather forms goes on; 



