162 
SCANDINAVIAN FISHES. 
30’9 /, while in Gymn. ventralis it is at least 33 %. The distance 
from the beginning of the first dorsal fin to that of the second in 
the first-mentioned specimen is 19'3 / of the length of the body and 
64'5 % of that of the head, and in the female specimen of Gymn. 
pistilliger 1 8 ‘ 9 % and 62'6 % respectively; while in the male speci- 
men of Gymn. ventralis it is 21 '8 % of the length of the body and 
83 % of that of the head, and, even in the specimen 43 mm. long, 
66 % of the length of the head. The base of the second dorsal fin 
in the male specimen of Gymn. pistilliger measures 82’6 % of the 
length of the head, in the female 84'8 %: in Gymn. ventralis this 
ratio may vary between 89 and 105 %. The least breadth of the 
interorbital space in the male specimen of Gymn. pistilliger measures 
66'7 % of the least depth of the tail, and in the female 80'6 %, 
while in the male the length of the rays of the ventral fins, the 
free part of which measures about 2 / 3 of their whole length, is 38 % 
of the length of the body. With the exception of the last two cha- 
racters and the singular dermal appendages, the other characters of 
Gymn. pistilliger , however, indicate a retention, in common with 
Gymn. ventralis , of juvenile characters, a point which shows that these 
species are very closely related. It is, therefore, natural that the 
young specimens and the fry of both species should present a still 
greater similarity in their characters. Thus, a male of Gymn. pistil- 
liger , 66 mm. in length, from Kara Sea, has a granulation on the 
top of the head _ which is harder than the slight trace thereof which 
occurs in the above-mentioned older specimens of that species, and a 
specimen 48 mm. in length, from the winter-quarters of the Vega 
Expedition, has an exceptionally small head, measuring only 26 % of 
the length of the body, while the length of the maxillary bones is 
34 % of the length ot the head. In every case, however, the other 
characters should be sufficient to decide the species. The coloration 
of the two species seems to be the same on the whole; but in the 
male of Gymn. pistilliger the first dorsal fin is blacker, with more 
distinct, round, white spots in one row along the superior margin, 
in another shorter one at the middle of the fin, and in a third along 
the base, while the ventral fins have distinct, black, transverse bands. 
All these points, however, may sometimes be observed, though never 
so distinctly, in male specimens of Gymn. ventralis. Whether Gym- 
nocanthus pistilliger occurs in the basin of the Atlantic, west of Nova 
Zembla, is a point on which we have no information. 
Gymnocanthus ventralis is an arctic and circum- 
polar species. It is of fairly common occurrence oft’ Spits- 
bergen, where it has been found by all the Swedish 
expeditions since 1837 (Sv. Loven), among the algte 
at depths sometimes as great as about 20 fathoms or 
even more". It is met with in similar places on the 
coasts of Greenland and Siberia. Since Lilljeboug 
found it in 1848 oft’ Schuretskaja (Russian Finmark), 
it has also been met with a few times oft’ the extreme 
north of Norway. In 1850 a specimen from Hammer- 
fest was forwarded to the Royal Museum by Mr. Bull. 
In these regions, according to Esmark 6 , it lives at as 
great a depth as 76 fathoms, or far below the belt of 
marine vegetation. It attains a size of from 215 c to 
250 d mm. Its food, in all probability, is chiefly com- 
posed of worms; but certain crustaceans ( Gammariclcc 
and Idotliece) have also been found in its stomach by 
Collett. Fabiiicius states, assuming that his obser- 
vations refer to this species, that in Greenland it lives 
on a sandy or clayey bottom, even where there is no 
vegetation; that it is more cautious and quicker in its 
movements than the true Cotti; and that the female 
lays its eggs among the ulvm, while the male is sup- 
posed to keep guard over them until they are hatched. 
Genus CENTRIDERMICHTHYS. 
Two distinct dorsal fins. Skin naked or with spines or scales. Head middle-sized. Uppermost preopercular 
spine lent or branched or with lateral spines. Palatine bones and vomer with teeth. Branchiostegal membranes 
united, with, a free transverse fold under the isthmus. No gill-slit behind the fourth branchial arch. Pays in the 
anal fin less than 20. 
Obs. Richardson gave this genus its name in 1844 b Though 
it had previously been formed by HeckeiV under the name Trachydennus , 
this name was unavoidably rejected, as it Dad already been used both 
among insects and reptiles. In later times both the Scandinavian 
species which belong to it, have received from KuOYER 6 ' the generic 
name Icelas. 
a In 1861 
Expedition 
b 
c 
d 
e 
f 
0 
The genus Centridermichthys, with teeth both on 
the palatine bones and on the vomer, so far as denti- 
tion is concerned, forms the most decided contrast to 
Gymnocanthus of all the Cottoids; but in other respects 
genus. The relations between 
been taken by the Norwegian Arctic 
is closely related to that 
it was taken in Hornsund at a depth of 60 .fathoms. According to Collett it has 
in Magdalene Bay (N. W. Spitzbergen) at a depth of 50 fathoms. 
Collett: Vid. Selsk. Forh. 1874, 1. e. 
according to LUtken. 
9, according to Collett. 
Voy. Sulph., Fishes, p. 73. 
Ann. Wien. Mus. 1880, II, p. 159. 
Naturh. Tidskr. Kbhvn, 2:den Rsekkes 1 :ste B. (184 1 — 45), p. 251. 
