288 
SCANDINAVIAN FISHES. 
which are above referred to, are sharply and easily distinguished by 
the larger eyes, the more tumid snout, the longer pectoral fins, the 
more anterior position (in most cases) of the ventral disk, and the 
black peritoneum of Cyclogaster Fabricii. But the transitions deprive 
these characters of their value, and the dubiousness of these varieties 
is forced upon us, especially when we have to decide to which of 
them the Baltic form should be referred. We have already® declared 
our opinion, when arranging the collection of fishes made by the Vega 
Expedition in the Arctic Ocean off Siberia, that Cyclogaster Fabricii 
is a variety of the Common Sea-Snail, and a new examination of all 
the examples of this species belonging to the Royal Museum has still 
further strengthened this impression. 
The Common Sea-Snail attains a considerably greater 
size than the preceding species, but only in its true 
home, the Arctic Ocean, where it may be at least 275 
mm. long. In Sweden, however, it scarcely ever exceeds 
half this size. The form of the body is essentially the 
same as that of the preceding species; but the caudal 
part is still more compressed, and its outlines converge 
more sharply towards the caudal tin, the least depth 
of the tail varying between 3 and 4 1 j 2 % (3'1 — 4‘2 %) 
of the length of the body. The head is generally larger 
in this species than in the preceding one, its length in 
most cases being about l / i (from 24 to 27 %) of that 
of the body * 6 . The eyes are also larger, but vary con- 
siderably in respect of size. They are, as usual, rela- 
tively larger in young specimens than in old — in a 
specimen 19 mm. long, from the Baltic, the longitu- 
dinal diameter of the eye is 8‘4 % of the length of the 
body and 31 '3 % of the length of the head, in middle- 
sized specimens (under 100 mm. in length) the usual 
size of the eyes is 4 or 5 % of the former and from 
15 to 20 % of the latter, while in the largest specimens 
(170 mm. or more in length) it may sink to 2 1 / a % of 
the length of the body and 10 % of the length of the 
head. We also find, however, that in the variety which 
has received the name of Cyclogaster Fabricii , the large 
eyes are generally persistent, their longitudinal diameter 
varying between 6 and 8 % of the length of the body 
and 1 8 and 28 % of the length of the head. The breadth 
of the interorbital space also varies considerably, be- 
tween about 7 and 14 % of the length of the body, 
but is generally greater than in the preceding species. 
The anterior pair of nostrils are rather high and tubu- 
lar, the posterior generally appear merely as transverse 
slits on each side, at the side of the anterior upper 
corner of the eye, but the margin of these slits is also 
considerably raised in some instances. Among the jaw- 
teeth, which with this exception resemble those of the 
preceding species, Lutken found, in old specimens, some 
simple (single-pointed) teeth, like those which Stein- 
dachner (1. c.) has described in the Californian species 
Cyclogaster ( Liparis ) pulchdlus and Cyclog. (Neolip ar is) 
mucosus. The character which has been derived from 
this peculiarity, and employed as a generic distinction 
between this species and the following one, thus loses 
its validity. The nature of the skin and the extension 
of the system of the lateral line, on the head and the 
body, are the same as in the preceding species. Of 
the lateral line on the body there generally appear, in 
this species too, only the first two pores (ducts); but Lut- 
ken has described perfect lateral lines, though with some 
distance between the pores, in Cyclogaster Fabricii , and 
the lateral line is also complete in the largest specimens 
of the common form from Spitsbergen. The small, 
round, granular plates on the skin are more common, 
especially on the head and the front part of the back, 
in this species than in the preceding one. 
The pectoral fins are generally longer than in 
Montagu’s Sea-snail, especially in the Baltic form and 
Cyclogaster Fabricii, where their length from the upper 
angle of the insertion to the tip of the longest rays 
may rise to 20 — 25 % of that of the body. In young 
specimens, however, in this species also, their length 
is no more than 15 % of that of the body. The dorsal 
and anal fin are distinguished from those of the pre- 
ceding species — apart from the greater number of the 
rays, which has already been remarked — partly by 
the fact that the descending curve in the margin of the 
former is much less marked, sometimes quite imper- 
ceptible, in this species, and that the longest rays of 
these fins are situated somewhat farther forward, and 
partly by the fact that both these fins are continued 
much further out on the caudal fin, and in Arctic spe- 
cimens which are normal in other respects, are some- 
times so closely united to the latter, that the line of 
demarcation between them is externally invisible. We 
find an example of this in Cyclogaster lineatus as first 
described by Lepechin; and the species thus departs 
considerably from the form common in more southern 
localities, which in this respect sometimes comes very 
near Montagu’s Sea-Snail — so near that this character 
« Fish. Exhib., London 1883. 
6 Only excejrtionnlly have we found the length of the head so small as 22 % of that of the body; and these exceptions may well be 
due to the difficulty of taking sure measurements from the loose tip of the snout. 
