HOUGH DAB. 
while only female characters are given in the other two. If we 
eliminate this disturbing influence from the comparison, the result 
becomes still clearer: Drepanopsetta platessoides represents the highest 
stage of development of the female characters. 
If we now compare this table with that given above (p. 407), 
which shows the relation between the four forms of the Plaice group, 
vie find that, in 12 of the 16 relations there given, as soon as the 
percentage is greater in Fleur, glacialis than in Fleur, cicatricosus, 
or when the percentage is greater in Fleur, platessa than in Fleur, 
flesus, the percentage in Drepanopsetta platessoides is also greater 
than in D rep tin. limandoides , while, when the percentages run in the 
opposite direction, the case is reversed. Again, just as Pleuronectes 
glacialis is a more strictly Arctic form than Fleur, cicatricosus , so 
also Drepanopsetta platessoides, as being a Greenland form the south- 
ward range of which is bounded by the southern termination of the 
Arctic current that follows the east coast of North America, may be 
regarded as a more Arctic form than Drepanopsetta limandoides , which, 
it is true, goes as far north as Spitsbergen, but is also found at least 
as far south as the south-west point of England, where no current 
can explain the occurrence of Arctic forms. Thus, the original form 
of this group, too, has probably belonged to the Arctic fauna. 
With these reservations, and until a more extensive supply of 
materials for examination may perhaps put this question in another 
light, we adopt the opinion first hazarded by GOnther and subse- j 
quently more deliberately weighed by Collett, that both these forms J 
may be included under a common specific name. Among the syn- 
onyms of the species Brown-Goode and Bean also give Stoker’s 
Platessa dentata , though he states (Mem. Amer. Acad. Arts., Sci., | 
u. ser., vol. VIII, part. II, p. 391) that in its case the dorsal fin 
begins just over the middle of the ege , an expression which, if we 
adopt the synonym, must not be taken too literally. 
On the coast of Scandinavia the average length of 
the Rough Dab is 22 — 25 cm., though it is sometimes 
29 — 32 or even 35 cm." long. Apart from its large 
mouth, the species shows a general resemblance to the 
Dab (PI. limanda ); and it is from this that the name 
of limandoides is derived. In the form which occurs in 
Scandinavian waters the greatest depth of the body is 
about 7s of the total length, and the greatest thickness 
about 1 j i of the greatest depth. The length of the head 
measures about V 4 ('26 %) of the length of the body 
to the base of the caudal tin. The dorsal edge of the 
head slopes evenly downwards from the beginning of 
the back. The eyes are exactly the same in form and 
structure as in most of the Flounders; they are almost 
equal in size and are set on the right side, the upper 
scarcely Vs of its length behind the lower. The length 
of the latter is in young specimens somewhat greater 
than, in old about equal to, the distance between it 
and the tip of the snout; and its hind margin lies at 
about the end of the second fifth of the head, 'file 
inner side of each eye (the side nearest the other eye) 
is somewhat more raised than in most Flatfishes, the 
423 
position of the iris being thus more nearly vertical, and 
the pupils being turned in opposite directions. This is 
a similar arrangement to that which enables the Rat- 
fishes in general to see both to the right side and the left 
without any special exertion, when they are lying with 
the blind side on the bottom, and which is supple- 
mented by the great mobility of the eyes. In this 
species the interorbital space forms a. narrow carina, 
somewhat higher than usual, which, in spite of this, 
disappears as we follow it backwards. The nostrils of 
each pair are distinctly separated from each other. On 
the eye side the anterior nostril, which is obliquely 
raised into a tubular form, lies just at the edge of the 
cheek-fold (the lower margin of the preorbital bone) 
above the maxillary bone, while the posterior, which 
is without raised margin, is situated somewhat higher 
up than the anterior, almost in the line drawn between 
the anterior margins of the eyes, but nearer to the 
lower eye than to the upper. The nostrils of the blind 
side, which in other respects resemble those of the eye 
side, lie somewhat nearer each other, in a straight line 
with the base of the dorsal fin, the anterior being situ- 
a, ted about half-way between the lower margin of the 
preorbital fold and the beginning of the dorsal fin, or 
somewhat nearer the former. The mouth is fairly large, 
this being the most striking difference between this 
species and the true Flounders; and the upper jaw-bone 
is so long that, if bent upwards above the lower eye, 
it would extend to the hind margin of the latter. The 
teeth are conical and pointed, especially on the inter- 
maxillary bones; small, but in front, especially on the 
intermaxillary bone of the eye side, larger; and ar- 
ranged in a. single, rather irregular row, at intervals 
about equal to the breadth of a tooth. On the eye side 
they are recurved and behind smaller, but are present 
along both jaws, except in the hindmost part of the 
lower jaw. In this species as in most of the Flatfishes, 
the two transverse dermal folds (palatal curtains) within 
the rows of teeth, both in the upper jaw and the lower, 
are broad and resemble true vela'. The gill-cover is 
free, as usual, above the pectoral fin and across the 
posterior opercular corner. The margin of the bran- 
chiostegal membrane is not folded back so far as in most 
of the Scandinavian Flatfishes. This is the only Scandi- 
navian species of the Flounder-series that has 8 bran- 
ch iostega.1 rays, 7 large and somewhat flattened ravs on 
a On the English coast, according to Day, a specimen 38 cm. long has been found. 
'' For the function of these folds, see above, p. 263. 
