ARCTIC FLOUNDERS. 
407 
north of North America, the second north of Asia, and 
the third straight across the Atlantic. The first two 
gaps are tilled, at least in part, by the variety PI. 
glacialis, which seems to lie a purely Arctic form, while 
PI. cicatricosus, of the White Sea and the coast of 
Alaska, lives in a comparatively milder Arctic climate. 
On the west coast of the United States the geographical 
range of the latter species extends much further south, 
in common with that of several other Arctic species, 
which, on account of the set of the ocean-currents, may 
there appear in much more southern latitudes than on 
the east, side of the Atlantic. 
Though Pleuronectes glacialis has not been found 
within the true limits of the Scandinavian fauna, in 
spite of the fact that it lives in their immediate vici- 
nity, still it is of especial interest from a systematic 
point of view, as the relations between its two forms 
throw a considerable light on those between the Floun- 
der and the Plaice. As it is also easier for us in this 
way to gain a general view of the relation between 
these species and the Dab, we here give a table of 
averages for the most important characters of these 
five forms: 
Average in 
Pleuronectes 
limanila. 
Pleuronectes glacialis. 
2. ^ 
1 IT 
2. o 
O 
O rs 
cc rs 
ce 00 
Pleuronectes 
platessa. 
Pleuronectes 
flesus. 
tf + 9 
cf + Q 
c? 
9 
$ 
tf + Q 
(fl + 9 
Length of the body, expressed in millimetres... 
— 
23(5 
198 
204 
194 
195 
297 
269 
„ „ „ head... 
in % of the length 
of the 
body 
20.7 
22.5 
— 
— 
24.3 
23.o 
24.0 
Greatest depth of the body - 
11 11 11 11 11 
11 11 
,, 
38. n 
43.9 
41.5" 
45.2 
39.2 
40.8 
41.i 
Least ,, 
, „ „ 
11 11 
8.5 
9.6 
— 
— 
9.4 
7.9 
7.5 
Postorbital length of the head 
„ „ 
11 
12.2 
15.5 
— 
— 
16.7 
15.5 
Kit 
Length of the head in 
°/o of the greatest depth 
of the body 
f)3.o 
51.5 
— 
— 
61.7 
56.6 
58.5 
Postorbital length of the head ,, 
H 5? 11 11 11 
„ ,, 
„ 
31.4 
35.5 
— 
— 
42.5 
38.o 
39.i 
Length of the branch of the lower jaw on the blind side . 
in % of the length 
of the 
body 
8.3 
7.8 
— 
— 
8.5 
8.2 
8.4 
», » „ „ „ „ , „ ,, „ eye ., . 
11 11 11 11 11 
„ „ 
,, 
7.7 
7.3 
— 
— 
7.8 
7.0 
8.i 
,, .. base of the dorsal tin 
11 11 11 11 11 
(58.6 
(59.7 
— 
— 
09.5 
69.5 
6(5.8 
., ., ., anal ,, 
11 11 
53.o 
50.5 
— 
— 
48.3 
1)3.2 
4(5.5 
„ ., longest ray in the dorsal fin 
,, j, ,, 
11 11 
,, 
11.7 
11.4 
13.i'' 
10.3 
10.7 
11.3 
12 i 
•• •> •• - anal 
„ ,, ,, ,, 
11 11 
11.7 
11.8 
13. 4 C 
10.9 
10.7 
11.6 
12.5 
Distance between the anal fin and the tip of the snout 
11 11 11 11 11 
11 11 
30.4 
34.4 
— 
— 
34.8 
30.6 
35.8 
Length of the pectoral fin of the eye side 
11 11 11 11 11 
11 11 
13.0 
13.3 
15.9 ■' 
11.7 
12.8 
10.1 
11.5 
., „ ,, ventral „ ,, „ ,, 
11 11 
.. 
7.s 
9.o 
10.U 
8.5 
8.3 
8,i 
7.7 
,, ,, ,, middle rays of the caudal fin _ 
,, ,, ,, 
11 11 
,, 
17.9 
17.1 
18.2' 
1(5.5 
16.8 
18.6 
17.2 
Fla is table, which also contains the appreciable 
sexual differences in var. FI. glacialis ( franklinii ), shows 
n the first place that in the great majority of cases 
where the percentage in PI. glacialis is higher than in 
PI. cicatricosus , the percentage in PI. platessa is also 
higher than in PI. flesus, and that where it is lower in 
the first form than in the second, it is also lower in 
PI. platessa than in PI. flesus. Thus, in most cases 
the difference of form in the first two varieties runs 
in the same direction as in the last, two species. If 
a Maximum 
percentage 
in cf <7 43’0. 
Minimum 
1 1 
„ ? > 43-0. 
h Minimum 
i? 
„ <? > 12-0. 
Maximum 
11 
„ ? < 12'0. 
c Minimum 
„ 
„ & > 12-0. 
Maximum 
11 
„ $ < 12-0. 
d Minimum 
11 
„ d* > 15.0. 
Maximum 
11 
„ 9 < 14-0. 
e Minimum 
11 
„ a*> 9-0. 
Maximum 
11 
., ? < 9-0. 
f Minimum 
11 
„ o" > 17-2. 
Maximum 
11 
„ $ < 17-2. 
