640 
SCANDINAVIAN FISHES. 
together form an elongated horse-shoe, equal in length 
to the space between 9 of the free spinous rays on the 
back. Within each arm of this horse-shoe projects a 
small portion of the anterior extremity of one of the 
pelvic bones. The two pelvic bones are also elongated 
and narrow in this species, their length being about 
equal, in adult specimens, to the space between 10 or 
even 11 of the free dorsal rays. They are thin and 
almost flat, the inner surface alone being slightly hol- 
lowed into a broad channel; and they are strengthened 
along the middle by two ridges, an outer and strong 
one and an inner and weaker, which is interrupted 
at the middle. Above, towards the side of the body, 
their thin margin is only slightly broadened at the 
middle, and they do not send out any special branch 
in this direction. Inwards, on the other hand, at the 
lower ventral edge, at the middle of their length and 
a little further back, they send out a flat and thin 
process, somewhat wider towards the tip, which meets 
the corresponding process of the pelvic bone from 
the other side of the body, though without entering into 
any firm osseous connexion with it. The pelvic bones 
extend very nearly to a line with the vent; and here 
this angular structure of the ventral edges ends, to be 
replaced at the base of the anal fin and on the under 
surface of the tail by a row of plates analogous to that 
we have just seen on the dorsal side. The plates of 
the lateral line, about 40 in number, fastigiated and 
carinated, with the carinae partly covering each other, 
form a straight row from the temporal region above 
the gill-cover out along the lateral edges of the com- 
pressed tail, though here they grow thin and indistinct. 
The first free spinous ray on the back is set above 
the hind part of the gill-cover, at a distance from the 
tip of the snout measuring between 24 1 / 2 and 22 % 
(generally decreasing with age) of the length of the 
body. The last (hindmost) of these spinous rays lies 
exactly opposite the vent, and the distance between it 
and the tip of the snout varies individually between 
45 and 46 % (exceptionally 43 %) of the length of the 
body. Thus, during youth, the space occupied by these 
spinous rays is, as a rule, somewhat less, in old spe- 
cimens somewhat greater, than the distance between the 
first ray and the tip of the snout. The length of the 
rays is somewhat greater than the distance between 
them; and their articulations lie a little to one side 
and in a zigzag, so that, when they are depressed, the 
tip of each ray falls beside the base of the next ray 
behind it, in the groove formed by the above-mentioned 
concave plates". Just behind the last spinous ray rises 
the true dorsal fin, triangular, with rounded apex, the 
first ray being somewhat shorter than the second, but 
equal in length to the third, the other rays decreasing 
in length gradually, but sharply. Sometimes both the 
first and the second rays are simple, but in most cases 
all the rays are more or less deeply branched. The 
last ray is united throughout its length by the fin- 
membrane to the dorsal edge. When erected, the rays 
are recurved, the anterior (as well as the posterior) 
side of the triangle being thus convex. The length of 
the base of the fin is about 1 / 2 (varying between 56 
and 47 %) of that of the head. Just in front of the 
anal fin we find a free spinous ray 6 , equal in size 
to the last spinous ray on the dorsal edge, but situated 
further back, vertically below the first or even the 
second ray of the true dorsal fin. Thus, the anal fin 
being almost exactly similar to the dorsal in form, 
structure, and size, the termination of the former lies 
somewhat further back than that of the latter. The 
form of the caudal fin reminds us, to a certain extent, 
of a combination of the anal fin with the true dorsal, 
in which combination each of these fins would cor- 
respond to a half of the caudal fin, which is fan-shaped 
when expanded. In this species, as in all the Scandi- 
navian Sticklebacks, this fin contains 12 rays, excluding 
a few (generally 2 or 3) small supporting rays at each 
margin), among which the 10 middle ones are branched 
for about half their length, but the outermost simple. 
The middle rays of the caudal fin are always some- 
what, though sometimes only slightly, shorter than the 
longest rays of the dorsal fin, and measure about 8 C 
or 9 % of the length of the body. 
The pectoral fins are of the form and structure 
common to all the Sticklebacks. As a rule they consist 
" When the number of these rays is less than usual, it is generally the 14th that is wanting, as KR0YER has remarked, the distance 
between the last ray and the last but one being thus greater than that between the other pairs. The interspinal plate of the absent ray is 
also wanting. In such specimens we have also found the third spinous ray considerably reduced, and its interspinal plate proportionately 
smaller than the others. In some cases Heincke found only 13 free spinous rays. 
h In our figure this ray has unfortunately been overlooked. 
c Sometimes 7. 
