FIFTEEN-S PIN ED STIC IvL EB A C K . 
639 
length of the snout is exactly equal to the distance 
between the hind margin of the eye and that of 
the operculum. This elongation of the snout is, how- 
ever, a character of growth, for in fry 21 mm. long 
the length of the snout is about 60 % of the post- 
orbital length of the head, in young specimens between 
50 and 75 mm. long about 90 % thereof. The elonga- 
tion is produced, as we have mentioned above, by the 
growth in a forward direction of the ethmoidal region 
and the palatine parts as well as of the preoperculum 
and interoperculum. At the same time the quadrate 
bone with the articular knob for the lower jaw moves 
forward, and the cleft of the mouth, which up to the 
present has been comparatively larger and almost hori- 
zontal, becomes relatively smaller and rather more 
ascending. With this elongation is also connected the 
relative diminution of the eyes; in a specimen 21 
mm. long their longitudinal diameter is equal to 
the length of the snout, in specimens 25 mm. long 
about 3 / i , in specimens 50 mm. long about 2 / 3 , and in 
a female 172 mm. long only slightly more than 1 / 3 
of the same length. 
The head is quadrangular, tapering in a. forward 
direction, with perpendicular sides and only slightly 
convex occiput. The snout is depressed and blunt, 
with the upper profile slightly concave. The eyes are 
round, and their superior margin lies on a level with 
the flat or somewhat hollow forehead, or rises a very 
little above the latter, the breadth of which, at the 
anterior margin of the eyes, is equal to their diameter. 
The small, round nostrils, only one on each side, lie 
half-way along the snout. The edges of the mouth are 
furnished with fleshy lips, lobate on the sides of the 
upper jaw; the lower jaw projects beyond the upper, 
which may, however, be protruded by means of the 
long nasal processes of the intermaxillary bones. The 
length of the lower jaw is about 1 / g that of the snout. 
When the mouth is closed, the small maxillaries, the 
length of which is about 1 / g that of the intermaxillaries, 
drop under the projecting preorbital bones. The jaw- 
teeth are of equal size, chisel-shaped, and most of them 
notched at the margin; they are set in front in several 
(3 or 4) fairly regular rows, behind in a single row. 
The pharyngeal teeth are pointed, and above they form 
on each side an almond-shaped card, obliquely divided 
into an anterior, smaller patch and a posterior, larger 
one. The gill-rakers are setiform, 10 or 11 in number 
on the first branchial arch. The pseudobranchiae lie 
high, on each side within the articulation of the hyo- 
mandibular bone; each of them is made up of five, 
digitiform lamellae, set in a transverse row. The pala- 
tine fold of the upper jaw is fairly large, the corres- 
ponding dermal fold in the lower jaw less developed. 
The external bones of the head are granulated and 
striated. The operculum is triangular, with the hind 
inferior side somewhat convex, the upper side soine- 
Avhat concave. The suboperculum has a short, anterior 
branch in a vertical direction and a longer, posterior 
one, broader below, tapering behind, and curved like 
a sabre; the latter forms the whole opercular margin 
along the lower posterior side of the true operculum. 
The preoperculum forms a right angle, with the an- 
terior, horizontal arm, which is coasted by the subjacent 
interoperculum, considerably elongated, as we have 
mentioned above. The two posterior suborbital bones 
are attached to the upper (inner) margin of this arm, 
the posterior firmly, the anterior very loosely, thus 
forming a cuirass for the cheeks, but only under the 
eyes. The hind part of the cheek (between the eye 
and the vertical arm of the preoperculum) and the space 
between the long preorbital (first suborbital) bone and 
the anterior part of the horizontal arm of the preoper- 
culum (a strip along the side of the snout, behind the 
corner of the mouth) are covered by the glossy skin 
alone. The gill-openings extend above the operculum 
for a distance measuring about V 3 of its length. Under- 
neath the branch iostegal membranes are united into a 
broad, free fold, the hind margin of which coincides 
with the anterior end of the interclavicles. 
The form of the trunk is determined principally 
by the granulated plates that follow the dorsal margin, 
the lateral line, and the ventral margins. The dorsal 
margin is occupied by the plates that have been deve- 
loped in the skin on the tops of the interspinal bones. 
Nearest to the occiput there lie two flat plates, one 
behind the other, followed by a row of concave plates, 
generally 15 in number, each of which is furnished 
with a free spinous ray with a small, triangular mem- 
brane behind it. Next follow seven plates, which 
support the true, soft-rayed dorsal fin. On the dorsal 
margin of the tail this row is continued by fastigiated 
and carinated plates, growing more and more flattened, 
and finally smoothed out and indistinct. The ventral 
edges are formed in the forepart of the body by the 
interclavicles, which are comparatively small in this 
species, and which by their arcuate union in front 
Scandinavian Fishes. 
81 
