MONTAGUS SEA-SNAIL. 
285 
was taken by Mr. C. A. Hansson off Stromstad at a 
depth of no more than a foot or so. 
In adult specimens in general the length of the 
head is equal to the greatest depth of the body, or less 
than the latter, sometimes sinking as low as 19 % of 
the length of the body. In the fry it is, as usual, 
relatively greater". The eyes are small, their longi- 
tudinal diameter, in adult specimens from 40 to 80 mm. 
long, varying between I (1 and 1 4 % of the length of 
the head, or between 55 and 44 % of the breadth of 
the slightly convex interorbital space, or between 55 
and 75 % of the least depth of the tail. The blunt and 
in most cases, convex snout, the length of which is 
rather more than 1 / 3 of that of the head, is furnished 
superiorly, in front of the eyes and somewhat nearer 
the middle of the head, with two tubular nostrils; and 
behind the latter, just within the upper anterior corner 
of the eye, there sometimes appears in young specimens 
a small hole or transverse slit on each side, forming 
the posterior nostril, but in most cases closed, covered 
by the skin, and visible only as a small dermal pro- 
tuberance. The mouth, which lies at the very tip of 
the snout, with the upper jaw projecting only slightly 
beyond the lower, is small, but fairly broad, the breadth 
of the gape, which is horizontal, measuring about half 
the length of the head. The dental card on the inter- 
maxillary bones, as well as that in the lower jaw, is 
broad (containing many rows) in the middle, the teeth 
being tricuspid, with the middle point longest. The 
lips, both the upper and the lower, are each furnished 
with a row of pores along the margin, generally con- 
taining 4 pores on each side, and from the upper lip 
there also runs, in the direction of the nasal region, a, 
row of two similar pores on each side. The further 
extension of the system of the lateral line on the head 
is externally visible in the pores round the eyes, and 
in a row which is the only external indication of the 
margin of the preoperculum; but of the lateral line 
proper we find only two pores on each side, just above 
the upper corner of the gill-opening. The latter is a 
perpendicular slit, the lower third or fourth of which 
lies just in front of the upper part of the base of the 
pectoral fin. The length of this slit, however, varies 
considerably, between §/ 2 and V 4 of the length of the 
head. The anterior margin of the slit, or the oper- 
“ In a male 71 mm. long, from Bohuslan, the length of the 
same locality, the length of the head is 27'8 0 /o of that of the body. 
cular margin, projects at. about the middle into a more 
or less obtuse dermal flap, which fits into the upper 
angle of the pectoral fin, and the thin frame of which 
is formed by the end of the elongated, triangular, forked 
or almost crescent-shaped operculum, together with the 
hind part of the subjacent, narrow and bent suboper- 
culum, which is of almost uniform breadth. The rest 
of the branchiostegal membrane is united to the skin 
of the body, but, forms a fold which hangs like a collar 
across the throat and the isthmus. This membrane is 
often so thin that one can easily count the six branchio- 
stegal rays on each side of the body, together with the 
interoperculum, which is of exacfly the same shape, 
and extends from the articulation of the lower jaw in 
a curve parallel to the lower posterior margin of the 
preoperculum. The interoperculum has often been 
reckoned by mistake among the branchiostegal rays. 
The pectoral fins are very broad at the base, which 
inferiorly curves forward, in a, direction parallel to the 
fold of the branchiostegal membrane and in front of 
the ventral disk, the pectoral fin on the one side being 
separated from that on the other by a distance no 
greater than the diameter of the eye. All the rays of 
these fins are simple and furnished with a fairly thick 
skin, the lower ones being free at the tip. The lowest 
rays are very short and only gradually increase in 
length ; but above the longest of them are a, few slightly 
shorter rays, the lowest part of each pectoral fin, with 
the tips of the rays turned outwards, thus resembling 
a distinct division or lobe of the fin. The upper part 
of the fin is obtusely rounded, the superior rays being 
of fairly uniform length. The length of the fin from 
the upper angle of the insertion is about 15 — 1 7 x / 2 % 
of the length of the body, and from the front part of 
the lower end of the base about 24 1 / 2 — 26 % thereof. 
When folded the pectoral fins extend to the perpendi- 
cular drawn just behind the vent, or even half-way 
between the latter and the beginning of the anal fin. 
The longitudinal diameter of the round or somewhat 
oblong sucking-disk formed by the ventral fins, together 
with its marginal fold, is about 11 or 11V 2 % of the 
length of the body and V 2 the length of the head or 
more. When the fish is in its normal state, this dia- 
meter is only slightly less or even equal to the distance 
between the disk and the tip of the snout; but when 
head is only 13'/o mm.; in a young specimen 18 mm. long, from the 
