38 MONOGRAPH OF THE FEESH WATER IH. 



In 1845, Mr. W. 0. Ajres wrote a somewhat extensive Memoir^ with a view of 

 demonstrating the identity between C. cognatus of Richardson, G. viscosus of Halde- 

 man, and Uranidea guiescens 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 American Cotti, Mr. 

 Ayi'es proceeds to establish the identity of this one and unique species, with the 

 European C. gobio. But we would ask, why should it be identical with G. 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 G. 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 G. 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 G. gobio of England; 

 others, that of the Seine ; still others, that of the Rhine, of the Danube, &c. &c., 

 and now, if these are, as we believe, types of several species, which can we call at 

 present G. 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 G. viscosus and G. cognatus are identified with G. gracilis 

 it is no longer possible to discern between specific cliaracters ; 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 G. cognatus and G. viscosus as two distinct species, as 

 they were previous to 1845. We erase the name of Cottus 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 sjpecies 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 a 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 ai'e a few more species which will be made known to science in the Ichthy- 



* Boston Journal of Natural History, v., p. 116. 



