436 
SCANDINAVIAN FISHES. 
The nostrils are set on the eye side in the mesial line 
of the nasal region in front of the eyes, the posterior 
nostril in a line with the anterior margin of the eyes, 
the anterior about the diameter of the pupil further for- 
ward. On the blind side they are set somewhat higher, 
but otherwise opposite to those of the eye side. The 
margin of all four is sometimes membranous and pro- 
longed, in the case of the two posterior nostrils, how- 
ever, only slightly and sometimes almost imperceptibly, 
lu the two anterior nostrils this membranous prolong- 
ation of the margin is so marked behind that it may 
fall forward like a lid and cover the whole nostril. 
At the anterior margin a small, narrow flap may be 
found. In young specimens, even at a length of 50 
mm., the eyes are still in a line with each other, or the 
upper eye may even lie somewhat further forward than 
the lower. This is a trace of the earlier stages of de- 
velopment, when the wandering eye first passed some 
way forward and then, when it had crossed the bridge 
of the snout, retired backwards on the eye side. In 
older specimens, on the other hand, at a length of 53 
cm. for example, the upper eye has sometimes moved 
so far back that its anterior margin is in a line with 
the middle of the lower eye. The eyes are fairly equal 
in size, their relative size decreasing as usual with age. 
In Turbots 50 mm. long the longitudinal diameter of 
the lower eye is 37 or 38 % of the length of the head 
behind it, while in Turbots 53 cm. long this proportion 
has sunk to about 14 %. The breadth of the inter- 
orbital space on the whole also undergoes relative de- 
crease, but to a much slighter extent; while until the 
fish has attained a length of 20 or 25 cm., this breadth 
increases not only absolutely, by growth, but in the 
above relation as well. In specimens 20 cm. long it 
measures about 19 or 20 % of the postorbital part of 
the head, but in specimens 53 cm. in length only about 
16 % thereof. In specimens 50 mm. long the breadth 
of the interorbital space is only about 7 a the longi- 
tudinal diameter of the lower eye, while in specimens 
53 cm. long it is 6 /s of this diameter. The length of 
the snout, measured from the anterior margin of the 
lower eye, is about 1 / i of that of the head. The pre- 
operculum is rectangular, rounded at the angle, and 
with the vertical prong about 1 / 3 longer than the hori- 
zontal. The operculum is triangular, like that of the 
Codfishes, with the hind lower side concave. Into this 
concavity the upper, narrower part of the suboperculum, 
the rest of which is of uniform breadth, is fitted, ex- 
tending so far that it penetrates the posterior dermal 
flap which forms the end of the gill-cover, just above 
the axil of the pectoral fin. The interoperculum is of 
fairly uniform breadth, but as usual grows narrower in 
front, its breadth behind being about 1 / s of the length 
of the upper jaw-bone. The branchiostegal membranes 
lie, as in most of the Flatfishes, in a deep fold below, 
where they meet and cross each other, most distinctly 
in old specimens. The innermost (foremost) of the seven 
branchiostegal rays in each membrane is not united 
at all to the corresponding ray on the other side, as 
we have found it in the preceding Flatfishes, but lies 
parallel to the other rays. 
The dorsal fin is furnished with a thick skin, and 
begins on the blind side, just above and in front of 
the anterior margin of the anterior nostril, exactly fol- 
lowing the dorsal edge throughout its length, without 
bending at all towards the blind side at its termination. 
As a rule the 30th — 35th ray from the beginning is 
the longest, its length being about 1 2 1 / 2 or 1172 °f 
that of the body. Measured in a straight line, the base 
of the dorsal fin occupies from about 71'/ 2 to 74 1 / 2 % 
of the length of the body. The fin contains 57 — 64 
rays, those in the anterior half of the fin being gener- 
ally simple or only indistinctly branched, while those 
in the posterior half are branched, sometimes with a 
simple ray inserted here and there. In young specimens 
the posterior rays are also simple or indistinctly branch- 
ed. The distance between the anal fin and the tip 
of the snout is at least (in the males) 30 % and at most 
(in the females) 35 or 36 % of the length of the body. 
The 17th or 18th (sometimes even the 21st) ray from 
the beginning of the fin is the longest, being generally 
equal in length to the longest ray of the dorsal fin; 
and to the structure of the rays the same remark ap- 
plies as in the case of the dorsal fin, with the addition 
that in this fin all the rays are still more frequently 
simple. Measured in a straight line, the base of the 
anal fin occupies about 58 — 597 2 0/0 °f the length of 
the body. There is no projecting spine at the begin- 
ning of the anal fin, which in young specimens and the 
males is included between the posterior parts of the 
insertions of the ventral fins, and has the vent close 
beside it on the blind side, just behind the end of the 
ventral fin. The genital opening lies just behind or on 
the outer side of the vent, and in the males is furnished 
with a small, pointed papilla at the anterior margin. 
The urethral opening, with its more or less distinct 
