III. COTTOIDS OF NORTH AMERICA. 7 



We may thus expect in Europe a number of species nearly equivalent to that 

 of America, and we shall find among them species with four soft rays to the 

 ventrals, and others with only three. Whether the lateral line will be found 

 extending to the tail in all of them, is a point worthy of attention. 



Let us return for a moment to Mr. Heckel's paper. Six species are found 

 mentioned there, of which four belong to Europe, C. gobw, microstomus, pcecilopus, 

 and affinis, arid two to America, C. cognatus and a new species which the author 

 calls C. gracilis. Now, in his synoptic list, this latter is the only one which has 

 but three soft rays to the ventrals, whilst the other five have four. Mr. Heckel 

 does not tell us whence he obtained the C. gobio which he had before him, which 

 would be of great importance to us, for we have seen that it is not perfectly iden- 

 tical with that of the Seine, since Cuvier allows to this latter only three soft rays 

 in the ventrals, and Mr. Heckel cites four of them. In the C. affinis the rays of 

 the ventrals are divided ; in C. gobio, microstomus, pcecilopus, and cognatus, they are 

 simple. The upper rays of the pectorals are branched in C. gobio and microstomus; 

 they are all undivided in the C. pcecilopus and cognatus. 



Thus we see Mr. Heckel borrowing the specific characters from the structure of 

 the fin rays. He says he has examined a large number of fishes in order to ascer- 

 tain the variations which the rays undergo during their growth. He has observed 

 that in his C. gobio, for instance, the bifurcation of the rays commenced only when 

 the fish had acquired half its size, whilst he has never seen the least trace of divi- 

 sion in the C. pcecilopus even at a size much beyond that at which the phenomenon 

 takes place in the C. gobio. From this fact he concludes that there are constant 

 characters of which we may avail ourselves for the distinction of species. He 

 denies the influence of climate on the division of the rays, as for instance, that this 

 division would take place under warmer climates, and he cites as a proof of the 

 contrary the G. pcecilopus, the most southern of his species, whose rays are undi- 

 vided, whilst they are branched in the more northern C. microstomus. 



When a genus happens to be as uniform as that of Cottus, it is a natural and 

 necessary consequence that we should take into consideration the minutest details 

 in discriminating the species. Did the Cotti present themselves uniform from one 

 extremity to the other of Europe, and were the species of America or of Asia more 

 diversified in their forms, there would be less reason for our undertaking so minute 

 a study of them. But their uniformity in all parts of the globe where they have 

 been observed is such as to lead us to researches of details ; for, howsoever a ques- 

 tion of that nature be definitively solved, be it in favor of a single species or of a 

 multitude, these researches will lead us to the understanding of the ichthyic signi- 

 fication of the genus to which they have reference, and to its distribution over the 

 surface of our globe. 



C. gobio, L. has been cited by Oth. Fabricius as an inhabitant of Greenland. 

 This is undoubtedly a particular species, which we shall mention hereafter. 



Again, C. gobio was thought to inhabit the United States, and as the present 

 labor was undertaken with a view to verify the assertion, we have no remarks on 

 this subject to make in this paragraph. 



The Cotti of Asia are little known, the centre of this great continent not having 



