BOREAL PEARL-SIDE. 
933 
species, but are curved in a sabre-like fashion through- 
out their length, and their supplementary bone, which 
is elliptical behind, projects in front in a tip that ex- 
tends to a line with the anterior part of the preorbital 
bone. Their median breadth is rather more than 1 / 3 
of their length, which is equal to that of the lower 
jaw, and less than 15 % of that of the body or than 
16 % of the length to the middle of the base of the 
caudal fin. In this last relation we have a character, 
constant to the best of our knowledge, to distinguish 
this form from the Mediterranean Maurolicus amethys- 
tino-punctatus, which is otherwise deceptively like M. 
Miilleri. The branches of the lower jaw are deep, but 
have an arcuate upper margin; and the symphysis is 
shallower than in Argyropelecus Olfersii and has a 
feebly developed chin-protuberance, which however pro- 
jects distinctly, when the mouth is closed, beyond the 
tip of the snout". As in Argyropelecus Olfersii, a 
sharp ridge runs along the outside of each half of the 
lower jaw, parallel to the thin inferior margin. The 
branches of the lower jaw approach rather near to 
each other at the inferior margin behind; but in front 
(behind the symphysis) the space between them widens 
into a clavate mentum (chin-space). The feeble den- 
tition of the mouth consists of small, pointed teeth, 
set in a single row and of uniform size, on the inter- 
maxillaries, on the hind (free) part of the lower edge 
of the maxillaries, on the upper edge of the lower jaw, 
as far as it is free when the mouth is open, and in 
an arcuate transverse row on the head of the vomer. 
There is no tongue; but the anterior (lower) part of 
the basihyoid bones forms a transversely-set rim, rising 
within the mouth like a tongue. The upper palatal 
fold is extremely narrow, the lower better developed. 
The pseudobranchiae are rather large, but consist of 
only 9 or 10 transversely-set, filamentous lamellae. 
The gill-rakers are set in one row, pointed, rather 
long, and so dense that they number about 30 on the 
front of the first branchial arch. The first gill- slit is 
long, the others rapidly decrease in length. The outer 
gill-openings are large in this species too, the two 
branchiostegal membranes being hardly at all coalescent. 
Above they extend to a level with the upper margin 
of the eye, below to a line with the anterior extremity 
of the preorbital bones. The branchiostegal rays are 
10, the first extremely small, the others slender, ex- 
cept the last (uppermost), which is broad and sabre- 
shaped. Among the thin bones of the opercular appa- 
ratus both the operculum and suboperculum are qua- 
drilateral, rectangular, the former being rather more 
than twice as large (deep) as the latter, but with the 
upper posterior angle rounded. In the lower margin 
of the suboperculum there is a rounded indentation. 
The interoperculum is more oblong, growing narrower 
in front, and lies along the lower arm of the pre- 
operculum. The preoperculum resembles a somewhat 
open (obtuse-angled) carpenter’s square, with both arms 
of nearly equal length. 
The dorsal fin is trapezoidal, with the upper pos- 
terior margin rapidly sloping. It begins at a distance 
from the tip of the snout measuring about 55 — 48 % 
of the length of the body. The length of its base is 
about 9 — 7 1 / 2 %, its height in front about 1 0 1 / 2 — 12 %, 
of the length of the body. The adipose fin, situated 
above the posterior part of the anal fin, is long and 
low, as in Argyropelecus Olfersii. The anal fin is much 
longer than the dorsal, but so deeply incised at the 
margin that its anterior part is almost similar to the 
latter fin, though much lower, while its posterior part 
is very low and of uniform height, only the last rays 
being slightly prolongated. Its distance from the tip 
of the snout is about 63 — 60 %, its base about 1 8 1 / a 
— 20 %, and its greatest height about 1 / 9 , of the length 
of the body. The caudal fin is forked, though not so 
deeply as in Argyropelecus Olfersii', its middle rays 
occupy about 7 — 8 % of the length of the body 6 . At 
the upper margin we have found 8 supporting rays, at 
the lower 5. The pectoral fins are bluntly pointed, 
semioval. Their length is about 16 — 14 % of that of 
the body. The ventral fins are of almost the same 
shape, but much shorter, their length being about 9 — 
10 % of that of the body, and only slightly greater 
than or even equal to the diameter of the eye. They 
are set at a distance from the tip of the snout measur- 
ing about 52 V 2 — 50 V 2 % of the length of the body, 
sometimes a little in front of, sometimes behind the 
perpendicular from the beginning of the dorsal fin. 
The preabdominal length is about 30 ( 31 a / 2 — 29 V 2 ) % 
a Both the maxillaries and the lower jaw are so thin arid transparent that the whole of the former and the upper posterior part of 
the latter are invisible in v. Wright’s figure. 
h In v. Wright’s figure, which evidently represents a fresh and perfect specimen, the caudal fin is much less forked than in our 
specimens. 
