62 MONOGKAPH OF THE FRESH WATER III. 



Mr. Heckel has placed the C. asjier in his genus Trachidermis, to which it bears 

 only analogies and no true affinities. The genera Trachidermis and Cottopsis have 

 both a rough or prickly skin, and teeth on the palatine bones ; but Trachidermis 

 has the first dorsal, the mouth, the opercular spines, and the general shape of head 

 and body, of Acanthocotti. Cottopsis has the first dorsal, the mouth, the opercular 

 spine, the general shape of the head and body, of Cotti. The genus Trachidermis 

 is the diminutive of Acanthocotti, provided with a rough skin and teeth on the 

 palatines. The genus Cottoj)sis, on the other hand, is the amplification of Cotti, 

 provided with a rough skin, and teeth on the palatine bones. 



Besides all this, Trachidermis belongs to the marine tribe. Its relationships are 

 complete. 



Some time since. Sir John Eichardson made the genus Gentridermichtliys^ to 

 include two cottoids of the seas of China and Japan, with which he proposed to 

 associate his G. asper. But Centridermichthys we have shown to be identical with 

 Trachidermis, in which the marine species must be placed. 



COTTOPSIS ASPER, Girard. 



Syn. Cottopsis asper, Girard, Proc. Bost. Soc. Nat. Hist. III., 1850, p. 303. 



Coitus asper, RiCH. Faun. Bor. Amer. III., 1836, pp. 295, 313. PL 95, Fig. 1. 

 Tracliidermis RicJiardsonii, Heck. Ann. d. Wien. BIus. II., 1837, p. 162. 

 Centridermiclitliys asper, Rich. Ichth. of the Voy. of the Sulphur, 1844, p. 70. 



This fish we know only through the description and figures given by Sir John 

 Eichardson. Its ordinary size is from nine to ten inches, surpassing thus in size 

 all the fresh water species of the genus Cottus. To judge of the general form from 

 the profile view, the body would appear quite regular, diminishing gradually in 

 depth from before backwards. The back and belly are nearly straight and very 

 regular, until the termination of the dorsal and anal fins. 



The head forms the thii'd of the length, the caudal fin excluded. Its upper 

 surface is flattened or rather widely concave, without the least trace of ridges, 

 tubercles, or spines. The inferior lip projects a little beyond the superior one 

 when both jaws are brought close together. The mouth is broad, but not deeply 

 cleft. The palatine bones are furnished with teeth similar to those on the vomer, 

 pi'emaxillaries, and dentaries. 



The eyes are of medium size, and placed near the summit of the head ; yet the 

 distance which separates them above is more than one of their diameter. The 

 nostrils, situated on the same horizontal line with the eyes, are small and a little 

 nearer the snout than the oi'bit. 



The opercular apparatus, as far at least as We could understand it, does not 

 appear to differ much from that of Cotti. None of its constituent pieces are 

 serrated or provided with spines on their edge. The convexity of the preopercular 

 is armed with an acute spine, slightly curved upwards and covered by the skin so 



* Ichthyology of the Voyage of the "Sulphur," 1844, p. 74. 



