III. COTTOIDS OF NORTH AMERICA. 33 



CHAPTER III. 



ON THE GENUS COTTUS, Artcdi. 

 § 1. Zoological Characters. 



Eestricted within the limits which we have assigned to it/ the genns Cottus 

 still comprehends a considerable number of species which, although apparently cast 

 in the same mould, are nevertheless distinct, as will, we hope, appear from their 

 descriptions and figures. 



The characters of the genus consist in the presence on the preopercular of one 

 spine only, which is situated at the posterior angle of that bone, and is curved 

 upwards and backwards. Sometimes a much smaller spine is to be found beneath, 

 and in one instance there is a third one of the same size as the second, directed 

 downwards. The inferior edge of the subopercular is also provided with a similar 

 minute spine, having its point directed forwards, and generally com2Dletely concealed 

 under the skin and muscles. The head consequently has a smooth apjiearance 

 which contrasts singularly with the spiny head of Acanthocotti, or marine Cotti 

 of authors. The mouth is but little cleft, and its angles seldom extend beyond 

 the anterior rim of the orbit. The lips which line the jaws are capable of more 

 or less expansion along the branches of the jaws, and at the angle of the mouth. 

 The premaxillaries, the dentaries and the vomer, are the only bones provided with 

 truly characterized, although very small, card-like teeth. In their immature state 

 some species exhibit teeth-like asperities on the palatines. This occurs chiefly 

 amongst those having four jointed rays to the ventrals : in C. WiJsonii, G. Bairdii, 

 and G. meridionalis. G. gracilis is the only one of the division with three jointed 

 rays, where similar asperities have been noticed. This character of palatine teeth, 

 which is merely shadowed in the genus Cottus, acquires a full develojDment in other 

 genera, thus constituting a permanent feature and assuming an actual signification. 



The eyes are situated near the summit of the head, more or less approximated 

 on the frontal line. There are constantly two nasal openings; a tubular one, 

 placed along the space comprised between the anterior border of the eye and the 

 extremity of the snout; the other is even with the surface of the skin and situated 

 backwards, behind and above the former and very close to the orbit. The latter 

 opening has been but recently discovered, having generally been overlooked on 



» Proc. Bost. Soc. Nat. History, iii. 1851, p. 183. 



