COTTOIDS. 
163 
Centridermichthys ancl Gymnocanthus are in several re- 
spects similar to those which generally exist between 
the true Gotti and the fresh-water members of the 
family. In the former genus, for example, the mouth 
is larger and the anal fin shorter: the length of the 
maxillary bones is never less than 11 % of that of the 
body, and the length of the anal tin seldom exceeds 
25 % of the length of the body, i. e. the length of the 
maxillary bones is never less than 44 % of that of 
the base of the anal tin. However, just as we can 
scarcely draw a generic distinction between . the true 
and the fresh- water Gotti, we find, too, in the genus 
Centridermiclitliys, even in the two species of which we 
have now to treat, a distinct approach towards Gymno- 
canthus. 
In the basin of the Atlantic Centridermiclitliys , as 
well as the preceding genus, contains only forms which 
belong to the extreme north, but in the Pacific at 
least one species is found as far south as the Philip- 
pine Islands. The number of species is not great: only 
8 are known, most of them from the west coast of 
North America. 
CEN TRI DER MICI4TH YS U NCIN ATUS. 
Fig. 49. 
Skin naked , without scales or the corresponding spinous formations , hut sometimes with soft warts on the top of 
the head , as well as on the hack above the lateral line. The two middle spines of the preoperculum almost wanting 
or only slightly developed; the upper spine bent, pointing backwards in an upward direction , and often with a 
lateral spine at the base; the lower pointing forwards in a downward direction. Only two slightly-developed spines 
on the top of the head , corresponding to the posterior ( occipital ) spines in the other Cottoids. On the hind part 
of the maxillary bones a small, conical, dermal flap. A similar flap sometimes on the hind part of the skin which 
covers the upper part of the eyes. Head fairly low and flat , its length, from 28 to 30 % of that of the body. 
Length of the maxillary bones less than 12 % of that of the body, or from 57 to 60 % of that of the base of 
the anal fin. Length of the lower yaw less than 15 % of that of the body. Length of the base of the second 
dorsal fin less than 27 % of that of the body. Length of the base of the anal fin at least 80 % of that of the 
base of the second dorsal. Least breadth of the interorbital space less than half {from 30 to 40 % of) the least 
depth of the tail. Urogenital papilla of the male small 11 . Eggs few and large 0 . Coloration light oil-brown on the 
back, yellowish white on the belly: 3 dark-brown transverse bands on the dorsal side — in young specimens a similar 
band on the head above the orbital region — but these transverse bands are generally broken up into an irregular 
mass of spots. Dorsal , pectoral and caudal fins with similar transverse bands; anal and ventral fins of the same 
colour as the belly, but sometimes with transverse bands or spots. 
Fig. 49. Centridermichthys uncinatus , taken at a depth of from 5 to 10 fathoms, on a rocky, algous bottom, in Actinia Bay on the north 
coast of Taimyr Sound, in Aug., 1878. Temperature of the water at the bottom 29‘9° Fnhr. ; at the surface 33'6° Fahr. Natural size. 
Obs. The proportions given here, founded upon measurements 
of two males and two females, are intended to show, in comparison 
with the preceding genus and the following species, firstly, that the 
specific difference in Centridermichthys follows the same rules as in 
Gymnocanthus as described above, and secondly, that the characters 
of Centr. uncinatus, compared with those of C. havnatus, generally 
indicate a successive approach to Gymnocanthus. 
a It is, however, uncertain whether males ready to spawn have been examined. 
b In two females respectively 87 and 92 mm. in length, from the Arctic Ocean off Ljakoff’s Island (Siberia), taken in September, 
1878, the eggs were about 2 1 / 3 mm. in diameter. Collett (1. c.) estimated the number of the eggs in females taken by the Norwegian 
Arctic Expedition at about 60. 
