926 
SCANDINAVIAN FISHES. 
causes. In front of the dorsal tin the dorsal margin 
rises in a transparent, cartilagino-osseous carina, re- 
sembling an anterior, posteriorly ascending dorsal tin, 
but formed by the produced and coalescent tips of 7 
neural spines. The ventral margin, on the other hand, 
is sharpened at the isthmus, in the abdominal region, 
in the region of the anal tin, and just in front of the 
caudal tin, by the median carina between the rows of 
luminous spots situated at these points, a structure 
most nearly corresponding to the ventral carina of the 
Herrings. But between the ventral tins and the anal 
tin the ventral margin is channelled by a groove open 
below. In the rest of their extent the margins of the 
body are indeed thin, but blunt. The dorsal protile 
follows a fairly regular curve in front of the true 
dorsal tin, but from the beginning of this tin it slopes 
almost in a straight line, until, at the caudal tin, it 
becomes horizontal. The ventral profile is even more 
sharply curved in front than the dorsal; but behind 
the above-mentioned break it ascends at the same angle 
as that formed by the dorsal profile in its descent, 
though with a perceptible break at the end of the anal tin. 
The head is deeper than long. Its singular shape 
i due to the short snout, the vertically ascending cleft 
of the mouth, and the deep, but short opercular appa- 
ratus; and to these avc should add the comparatively 
deep isthmian region, which extends under the greater 
part of the length of the head. At the top the head 
is convex from the occiput to the snout, but flat and 
grooved in the middle, with a sharp, longitudinal ca- 
rina on each side, and strongly constricted between 
the eyes. Its length in an horizontal direction from 
the middle of the tip of the snout measures in our 
specimens about 28 — 29 % of the length of the body. 
The eyes are rather large and round, the vertical dia- 
meter being only a little greater than or equal to the 
longitudinal, and varying in our specimens between 
43 and 45 % of the length of the head, or about 1 / 8 
of that of the body. They are set high, their upper 
margin rising almost to the frontal plane, and so near 
to each other that the least interorbital width is only 
1 ,/ 4 of their vertical diameter. The postorbital length 
is only about 1 / 3 (32 — 34 %), and the length of the 
snout rather more than V 4 (27 — 28 %), of the length 
of the head; and the lower margin of the pupil lies 
on a level with the tip of the snout or a little higher. 
The suborbital ring is represented only by an extremely 
thin, oblong, lamelliform, and vertically set preorbital 
bone, which coasts the anterior margin of the eye. 
The nasal cavities are oblong, and lie close to the an- 
terior upper corners of the orbits and below the knob- 
shaped tip of the ethmoid bone. The nostrils are di- 
vided on each side by a thin, but flat septum of skin, 
without any elevation of the margin. 
The mouth ascends almost vertically, and the tip 
of the upper jaw projects slightly beyond the ethmoid 
(rostral) tip, but admits of hardly any protrusion. The 
nasal processes of the intermaxillaries are short, and 
the latter bones, each by means of its lateral branch, 
are so firmly united to and coalescent with the maxil- 
laries that the limit between them is distinct only in 
front, for a distance measuring about 1 j i of the dia- 
meter of the eyes. The motion of the intermaxillaries 
is thus reduced to a considerable extent: they can only 
follow the forward and backward swing of the maxil- 
laries. flow far the margin of the upper jaw is formed 
by the intermaxillaries, it is impossible to determine 
without dissection, an operation of which our materials 
have not permitted. But the whole margin of the up- 
per jaw is set with a row" of pointed, subulate and 
curved teeth, rather scattered and small, but of various 
sizes. The last four or five teeth'' are directed for- 
wards, the anterior ones pointing backwards. The ma- 
xillary bone, which is extremely thin, reminds us most, 
both in shape and structure, of that of the Herrings. 
Just behind (below) the constricted articular part it is 
curved like a sabre at the very margin of the mouth, 
but from this point back it is straight and of uniform 
breadth, forming an oblong rectangle. The median 
space, however, is not ossified, but consists of a silvery 
skin, distended between the true maxillary bone and its 
supplementary (jugal) part, which coalesces behind with 
the maxillary, and which extends, in the form of an 
osseous rod, forward to the articular part. The entire 
length of the maxillary is somewhat more than ’/ 4 
(about 26 — 29 %) of the length of the body, and its 
breadth in the oblong part about ] / 4 of its own length. 
The lower jaw is about equal in length to the maxil- 
“ Sometimes we find in front, on the intermaxillaries, a tooth or two lying inside or outside this row. 
6 Situated on that part of the upper jaw which, when the mouth is wide open, lies outside the branch of the lower jaw, and thus 
below the true cleft of the gape. In Argyropelecus hemigymnus the length of the intermaxillaries may be traced backward to this point, 
which there answers to about the middle point in the length of the maxillaries. 
