REMARKS ON THE COLEOPTERA. 241 



since I feel that one already conversant with entomological names 

 will find no difficulty in extending the already long list of parallel 

 species, while to the general reader, who desires only the deductions 

 of science, without entering upon the tedious processes by which 

 they are obtained, a catalogue of mere technicalities, which fail to 

 convey a single idea to his mind, will be equally useless and uninter- 

 esting. 



I purposed in the present essay to trace, as far as possible, the 

 mechanism of the agency by which the present distribution of species 

 has been effected, and to reduce its most obvious results to some fixed 

 principles. Fearful, however, lest my views should be considered as 

 derived exclusively from a consideration of insects, and their phe- 

 nomena of distribution, I prefer waiting until a sufficient familiarity 

 with other sciences will enable me to be less partial in my choice of 

 illustrations. I do this with the less regret as I find some of my 

 deductions are at variance with many of the most ancient, and most 

 firmly established prejudices of our nature, and before venturing any 

 assertion, which even in appearance deviates from " general impres- 

 sions," it is at least prudent to be supported by facts drawn from 

 more extended observation than is furnished by one or two limited 

 departments of knowledge. 



In the rapids at Niagara have been observed large numbers of 

 the singular animal described by Dekay (in the Zoology of New 

 York) as a new genus of Crustacea, under the name of Fluvicola 

 Herricki. They were attached to stones just below the surface of 

 the water, and crawled but slowly ; when seized, they endeavor to 

 contract themselves into a ball. 



These animals have a marvellous resemblance to the extinct group 

 of Trilobites, although, as will be seen in the sequel, they are the 

 larvse of an insect. Mr. Agassiz informs me that a similar form has 

 long been known to the zoologists of Continental Europe as Scutel- 

 laria amerlandica, but I have not been able to find any published ac- 

 count of it. 



On turning over some stones near the river bank, I was agreeably 

 surprised to find many specimens which had left the water for the 

 purpose of changing into pupae. The elliptical shield of the superior 



