38 MONOGRAPH OF THE FRESH WATER Iii. 
In 1845, Mr. W. O. Ayres wrote a somewhat extensive Memoir’ with a view of 
demonstrating the identity between C. cognatus of Richardson, C. viscosus of Halde- 
man, and Uranidea quiescens of Dekay. The individuals under examination, 
taken as a standard, were all secured in the State of Connecticut, and are indeed 
identical with the species described by Dr. Dekay. C. viscosus and C. cognatus on 
the contrary, are two other perfectly distinct species. 
After having referred to one and a single species, all the ners Cotti, Mr. 
Ayres proceeds to establish the identity of this one and unique species, with the 
European ©. gobio. But we would ask, why should it be identical with C. gobio, 
rather than with any one of the others found in Europe or Asia? Mr. Heckel’s 
investigations being not known in this country in 1845, Mr. Ayres was still under 
the impression that C. gobio was the only species of the genus in the old world; 
whence the idea of identifying with it those of North America. 
Without recapitulating here what we have said in the introduction, respecting 
the European Cotti, we may recall to mind that the C. gobio is not yet determined 
with accuracy, and that under such circumstances the comparisons lose somewhat 
of their value. Some have taken for terms of comparison the C. gobio of England; 
others, that of the Seine; still others, that of the Rhine, of the Danube, &ce. &e., 
and now, if these are, as we believe, types of several species, which can we call at 
present C. gobio? Had Mr. Ayres been aware of this state of things, he would 
have himself admitted, that it was more than premature to bring under this 
appellation, the American Cotti. 
It is evident that after C. viscosus and C. cognatus are identified with C. gracilis 
it is no longer possible to discern between specific characters; the idea of the genus 
alone is left to the mind. After this is done, you may read Artedi’s description, 
and nothing will be more natural than to find it agreeing perfectly with all existing 
Cotti. There is a generic identity and not a specific one. 
Thus, we shall consider C. cognatus and C. viscosus as two distinct species, as 
they were previous to 1845. We erase the name of Cottws gobio from the catalogue 
of fishes of the United States, into which it was too hastily introduced, recalling 
here to mind that wherever a complete study of the species of fish reputed identi- 
cal in both continents within the limits of the Temperate Zone has been made, the 
results have been that species differ from one continent to the other. Yet we 
would not allow any one to conclude them distinct @ priori, on this ground. We 
cannot, on the contrary, too much insist upon the necessity of direct observations 
and immediate comparisons. 
In 1850, appeared the descriptions of two new species brought from Lake Supe- 
rior, by Prof. Agassiz. 
Our own researches have made us acquainted with eight others, besides a ninth; 
which constitutes a new genus; so that the whole number of the Cottoid group 
included in the present work amounts to fifteen. 
There are a few more species which will be made known to science in the Ichthy- 
+ Boston Journal of Natural History, v., p. 116. 
