RIVER BULLHEAD. 
171 
jaw-bone is short and extends back only to a point 
vertically below the anterior margin of the eye. The 
length of the upper jaw-bone in the female is between 
77 a and 87 2 % of that of the body and in the male 
about 107a or in the former between 33 and 41 
and in the latter about 46 % of the length of the base 
of the' anal tin. The length of the lower jaw varies 
between 11 and 13 % of that of the body. The lips 
are thick and swollen, like the cheeks. The whole appea- 
rance of the head thus gains a close resemblance to 
that of the genus Gobius. The nostrils are small and 
open on each side into two tine ducts, as is usually 
the case in this genus; the anterior opening is the larger 
and is situated about half-way between the snout and 
the eye. In this, as in the other species of the genus, 
small cardiform teeth are set on the lower jaw, the 
intermaxillary bones and, in a curve anteriorly convex, 
on the head of the vomer. Underneath, from the lower j 
margin of the pectoral tins, the branchiostegal mem- 
branes are united to the breast, without any free der- 
mal fold across it; partly on this account and partly 
in the opercular flap, which is more deeply incised at 
the top, there is a slight resemblance, of which more 
hereafter, to the structure of the gill-openings in Cal- 
lionymus. The hind margin of the preoperculum is 
furnished at the top with a small, flat hook, turned 
upwards, but the interstice between the margin of the 
preoperculum and the point of the hook is filled by 
the skin. Below this hook — in which we may trace 
a fairly distinct likeness to the many-pointed preoper- 
cular hook in Callionymus , as well as to the corres- 
ponding structure we have seen in Centridermichthys — 
is another, slightly projecting, flat spine with broad 
base and blunt tip, which is generally very indistinct, 
though it varies in size. The lateral line, which is 
marked by about 33 small, short, porous openings, is 
without any armour and runs fairly straight forward 
from the caudal fin, at about the middle of the side, 
but below the first third of the second dorsal fin curves 
slightly downwards and then, in a line with the vent, 
gradually rises to such an extent, that at the margin of 
the gill-cover it is much nearer the back. The skin 
is smooth, scaleless and covered with a thick and tough 
mucus over the whole body. Even in this species, but 
still more commonly in the following one, we some- 
times find the anterior part of the sides — the part 
which is covered by the pectoral fins — sprinkled with 
small, spinous, scaly formations, which are more easily 
felt than seen. The two dorsal fins are united at the 
base, and the second is fairly long in proportion to the 
size of the fish — so long that there is only a short 
interval between the end of this fin and the beginning 
of the caudal fin. In the ventral fins we find a re- 
markable exception to the rule 'within the genus, na- 
mely that they have one ray more, i. e. they contain 
one spinous and four weak, articulated rays; the spi- 
nous ray is, as usual, closely joined to the first weak 
ray and hidden 1 >y the skin. The length of these fins 
is, as usual, greater in the male than in the female, 
but, so far as our observations extend, does not exceed 
177/2 0// ° °f the length of the body or 35 % of the dis- 
tance between the anal fin and the tip of the snout. 
I 11 the anal fin it is worthy of remark that the last 
two rays are close together at the base and that the 
base of this fin measures at most about 23 % of the 
length of the body. In the caudal fin, which is sharply 
rounded at the end, the 7 or 8 middle rays are qua- 
drifid or doubly bifid; in most cases too, in old speci- 
mens at least, there is one more bifid ray. Furthermore, 
in this species as in the following one, more at least 
than in the others, the rays of most of the fins, especially 
of the pectoral and ventral, have a tendency to divide at 
the point. This is visible only under a magnifying glass; 
to the naked eye, however, the rays seem simple. 
The coloration, as usual, varies considerably, from 
early youth, when the dark transverse bands which are 
general in the Cottoids, are more regular and distinctly 
marked. In adult specimens the body is of a grayish 
green colour, with irregular spots and transverse stripes 
of varying size and shape. The dorsal side is marbled 
with gray and brown right out on the snout. The lateral 
line is coasted underneath by some lighter, yellowish 
spots, which are more distinct in some individuals than 
in others. The rays of the caudal, the second dorsal, 
the anal and the pectoral fins are crossed by light streaks, 
which together form bands, partly broken and partly 
continuous, over the fins. These light transverse streaks 
give a broken appearance, as it were, to the rays. In 
the males the belly is of the same colour as the body, 
though somewhat lighter; in the females it is whitish. 
The ventral fins are generally without spots and of the 
same colour as the belly, but they are sometimes dotted 
or even spotted with black. The iris is dark, with a 
flame-yellow ring round the inner margin. The figure 
(plate VIII, fig. 1) is painted from a male, taken in the 
Baltic, in the month of July. 
