572 
SCANDINAVIAN FISHES. 
extend nearly to its extremity. The opercular appa- 
ratus as a whole is fairly large, but the operculum 
proper is the smallest part (about 1 / 3 ) thereof. The 
operculum is smooth, convex, triangular, and almost 
equilateral. The greatest part of the opercular apparatus 
consists of the suboperculum, which forms the whole 
of the inferior and posterior parts, and with its broadly 
rounded point projects somewhat behind and above the 
base of the pectoral tin. It is united to the operculum 
by an oblique, straight line; the lower margin forms 
a large, rounded sinus, to receive the base of the pec- 
toral tin; and the surface is smooth, with 9 distinct, 
radiating lines on the lower part. The four branchial 
arches are complete, and a -well-developed pseudobranchia, 
composed of from 12 to 14 threads, occupies the inner 
surface of each gill-cover. 
On the body itself Ave observe several longitudinal 
lines, first the lateral line proper, Avhich lies high on 
the back, the distance between it and the dorsal fin 
being about 1 / 2 of that between it and the median line. 
The lateral line is parallel to the dorsal tin, straight, 
and depressed in the rather large scales, each of which 
contains a branch of the muciferous canal Avith its 
opening. The line begins above the gill-cover, Avithout 
its usual external continuation on the head, and ends 
at the termination of the dorsal tin. — Along the middle 
of the sides there runs a someAvhat depressed median 
line along the middle angles formed by the aponeurotic 
septa of the large lateral muscles. This line is quite 
straight and consists of rather small dots, pricked, as j 
it Avere, Avitli a needle, and invisible Avithout the help 
of an ordinary magnifying-glass. They form an irre- 
gular double (or multiplex) toav, equal in Avidth to half 
a scale. The line resembles a lateral line, but is less 
marked and destitute of muciferous ducts. — On the 
sides of the belly Ave find a still more remarkable carina 
or dermal fold, which begins beloAv the base of the 
pectoral fin, folloAvs a perfectly straight course, and gra- 
dually disappears half-Avay between the vent and the 
caudal fin. Its height is about equal to the greatest 
breadth of a scale; it is thin and soft, and does not 
seem to contain any muciferous canal; but, in speci- 
mens preserved in spirits at least, it lies with the free 
margin bent outwards, covered by the mucus of the 
skin, and thus appears itself to surround a canal. — On 
the belly, between the tAvo lateral carina?, three fine 
longitudinal lines run from beloAv the pectoral fin to 
the vent, the tAvo lateral ones slightly depressed, but 
the middle one very fine, somewhat raised, of clear 
colour, and scaleless. In middle-sized specimens the 
anal aperture lies at the end of the third fifth of the 
length of the body, in the largest specimens a little 
farther back, its position thus groAving more posterior 
Avith age. It is only slightly, if at all, prominent, 
hardly more so than the smaller opening for the genital 
organs that lies behind it. 
The dorsal fin is of almost uniform height, its 
height in large specimens being scarcely half the depth 
of the body. It begins at the end of the first fourth 
of the body, or usually a little farther back, about as 
far (in young specimens someAvhat less, in old someAvhat 
more) behind the occiput as the latter from the tip of 
the snout. It ends some Avay from the caudal fin, the 
distance betAveen them being about equal to the least 
depth of the tail, or a little greater. The rays are 
about 56 in number, the variations being apparently 
confined to 2 or 3 more or less; all the rays are fine 
and articulated, but perfectly simple and pointed though 
not pungent. The membrane is thin and fragile. 
The anal fin begins just behind the genital opening 
and ends opposite to the termination of the dorsal fin. 
It is equal in height to the latter, and contains about 
30 rays of the same structure as those of the dorsal fin. 
The caudal fin is deeply forked; its greatest length 
is about equal to the depth of the body. It contains 
15 true (articulated) rays. Thirteen of these are bran- 
ched, though not very deeply, the outermost ray above 
and beloAv being simple and only slightly shorter than the 
corners of the fin. Outside these rays there lie several 
small, unarticulated or supporting rays: in a specimen 
3 dm. long Sundevall counted 1 1 above and 9 beloAv. 
In middle-sized specimens the pectoral fins do not 
extend further back than to the perpendicular from the 
first ray of the dorsal fin. In the very largest speci- 
mens they are relatively much shorter. In the speci- 
mens mentioned above, between 11 and 28 cm. long, 
the length of the pectoral fins varies Avith increasing 
age between 9 and 6 1 / 3 % of that of the body, from 
33 to 22 % of the distance betAveen the dorsal fin and 
the tip of the snout, or betAveen 81 and 56 % of the 
postorbital length of the head. They are also invariably 
shorter than the loAver jaw, their length varying with 
increasing age in the said specimens betAveen 88 and 
64 % of that of the latter. They contain 14 rays, all 
articulated; the first is simple and measures only slightly 
more than half the length of the fin, the second is in- 
