62 MONOGRAPH OF THE FRESH WATER IPD 
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Mr. Heckel has placed the C. asper 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 Cottopsis, 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 Richardson made the genus Centridermichthys' to 
include two cottoids of the seas of China and Japan, with which he proposed to 
associate his C. asper. But Centridermichthys we have shown to be identical with 
Trachidermis, in which the marine species must be placed. 
COTTOPSIS ASPER, Girarp. 
Syn. Cottopsis asper, GIRARD, Proc. Bost. Soc. Nat. Hist. III., 1850, p. 303. 
Cottus asper, Ricu. Faun. Bor. Amer. III., 1836, pp. 295, 313. Pl. 95, Fig. 1. 
Trachidermis Richardsonii, Heck. Ann. d. Wien. Mus. II., 1837, p. 162. 
Centridermichthys asper, Ricu. Ichth. of the Voy. of the Sulphur, 1844, p. 76. 
This fish we know only through the description and figures given by Sir John 
Richardson. 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 third 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, 
premaxillaries, 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 orbit. 
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 
1 Ichthyology of the Voyage of the “Sulphur,” 1844, p. 74. 
