ARGYROPELECUS OLFERSII. 
927 
laries. Each of its two branches resembles an acute- 
angled, isosceles triangle, with the short (hind) base 
turned downwards, where the angular part forms a 
projecting, spine-like angle. Within (above) and pa- 
rallel to the thin lower margin runs a ridge on the 
outer side. The symphysis is straight, and projects 
downwards in a chin-protuberance, channelled behind. 
Most of the teeth in the lower jaw, which are also set 
in a single row, are about twice as large as those in 
the upper jaw; but one of the anterior teeth on each 
side is considerably larger than the rest, and at the 
extreme front, where the teeth are of about the same 
size as in the upper jaw, they are more distinctly ar- 
ranged in a double row. The tongue is rudimentary, 
and the cartilaginous tip of the hyoid bone is smooth, 
without teeth. Only the upper jaw is furnished with 
a palatal fold, and this is not very broad. The vomer 
is toothless, but on the anterior part of the palatine 
bones, as well as on the upper pharyngeals, small teeth 
may be felt. The pseudobranchiae on the inner surface 
of the opercular and hyomandibular bones form an oblong 
patch, in which about 14 filiform, transversely set la- 
mellae may be counted. The gill-slits are large, ex- 
tending far forward in the mouth; but the upper parts 
of the hind branchial arches coalesce with the front side 
of the scapular arch, the hindmost gill-slit thus being 
closed above and rather short. The gill-rakers are long 
but scattered, numbering about 14 on the first branchial 
arch, besides a few small, hardly perceptible spines at 
the lower (anterior) end. Where the horns of the hyoid 
bone touch the tip of the basi-hyoid series (the lingual 
bone), they are furnished with an erect protuberance. 
The outer gill-openings are large, their upper angle 
lying on a level with the centre of the eyes, and the 
branchiostegal membranes being free from the isthmus 
arid united to each other not quite to the full length of 
the first branchiostegal rays, so that the anterior angle of 
the openings lies in about a line with the tip of the snout. 
The branchiostegal rays are slender and rod-like. The 
first six lie rather near each other, and the first of all is 
set close to the corresponding ray on the other side; the 
last three are somewhat larger and set further apart. 
The opercular apparatus, in accordance with the 
shape of the head, is characterized by its height. The 
vertical arm of the rectangular preoperculum is about 
three times as long as the horizontal. The preoper- 
cular angle is prolongated to a short, flat (thin), tri- 
angular spine, pointing downwards. The other oper- 
cular bones are extremely thin and flexible. The 
operculum is rectangular, but forms an oblique arti- 
culation above. Ifs surface is obliquely crossed by a 
ridge running from the anterior upper corner down- 
wards and backwards. Its breadth is equal to the length 
of the snout. At its lower margin lies the triangular 
suboperculum, with a more or less deep indentation 
behind. Below the latter and below the preoper- 
culum lies the interoperculum, which is divided into 
two parts, the anterior (below the preoperculum), 
elongated and united with the branchiostegal mem- 
brane only behind, the posterior quadrangular with 
rounded corners or circular, and entirely coalescent 
with the branchiostegal membrane, on which it lies 
like a scale. 
The greater part of the head, as well as the rest 
of the body, is covered with a thin, silvery epidermis; 
but the upper temporal region, between the eyes and 
the occiput, is naked, the surface of the bones being 
finely grooved and granulated. 
The fins resemble in quite essential respects those 
of the Hemibranc.hs and Lophobranchs. As in the said 
fishes, the soft rays, which are thin and transparent, 
with the tips strongly compressed in the longitudinal 
direction of the body, show but little developed rami- 
fication and have only scattered joints". In the sup- 
porting apparatus of the paired fins too, we find points 
that remind us most of the Sticklebacks. 
The true dorsal fin is obliquely rounded, the first 
rays being the shortest, but gradually increasing in 
length to the fifth or sixth, which is the longest in 
the fin. It begins at a distance from the tip of the 
snout measuring about half (50 — 51 %) of the length 
of the body, and the length of its base is about equal 
to the vertical diameter of the eye or a little greater, 
about 12V 2 — % of the length of the body. A little 
in front of this fin ends the fin-like osseous ridge 
formed by the projecting tips of 7* neural spines be- 
longing to the abdominal vertebrae, together with the 
thin and transparent, feebly ossified inferneural mem- 
“ We are indeed ignorant of the manner of locomotion employed by Argyropelecus Olfersii ; but from this structure of the fin-rays 
we may conclude that the fins perform their function by means of vibrations. This is the case, as we have seen above, not only in the 
Sticklebacks and Pipefishes but also in the Dory, where the second dorsal and the anal fins are furnished with similar rays. 
6 In Argyropelecus hemigymnus belonging to the 3rd— 9th vertebrae. 
Scandinavian Fishes. 
117 
