KAYS. 
1103 
aculei between them. In others, as in the Thornback, 
the two tins are farther apart, and the median line 
between them is armed with one or more spines. 
Of the coloration of the body Fries observed that, 
in spite of its variability, it is partly characteristic in 
some degree of different species — especially that of the 
under surface. As a natural result of the life led by 
the Rays, which are bottom-tishes, this side of the body 
is commonly light and colourless (whitish), and it would 
appear as yet to be uncertain whether the dark colour, 
entire or distributed in large spots, where it occurs on 
the ventral side, affords trustworthy specific characters 
or not. But good characters may be drawn from the 
sometimes distinctive coloration of the long winding 
canals and apertures of the ventral system of the lateral 
line, and these characters are of so much greater utility 
as being present from earliest youth and persistent in 
specimens either stuffed or preserved in spirit. The 
spots and ocelli which occur on the dorsal side of certain 
species, showing endless variation in size, colour, and 
extent, are utterly ..worthless as specific characters. 
With regard to the external differences of sex, 
which have long been known, Fries stated that they 
are, as usual, less marked in young specimens than in 
mature individuals, most of the male attributes being 
commonly absent or only rudimentary in the former, 
and developing in proportion as the age of puberty is 
approached. In general the females are armed with 
far more numerous and much larger spines than the 
males; but this rule is not without exceptions. 
Most of the true Rays are good and esteemed food- 
fishes. When boiled fresh, their flavour calls to mind 
that of the Halibut, or is not unlike that of lobster. 
They may also be dried and kept till required for use, 
in which case the fish is scored along the body. In this 
form they are usually eaten after having been lyed in 
the same manner as stock-fish. They are consequently 
sought after by the fisherman, and they are in general 
well distinguished and familiar to all, their vulgar 
names affording valuable aid in the definition of the spe- 
cies and their synonymy. Hollberg (1819) knew three 
Scandinavian species of the genus, the klorocka ( Raja 
radiata), knaggrocka ( Raja clavata, which he called 
prickrocka), and slatrocka (Raja batis). In his Prodro- 
mus (1832) Nilsson characterized four, the above-men- 
tioned species and the blagarnsrocka (R, Untea, which 
he called R. fullonica). In 1838 Fries added two, the 
gokrocka (R. fullonica) and plogjernsrocka (R. oxy- 
rhynchus). To these six species Malm supplemented in 
1857 the sandr ocka ( R. falsavela, which he called spdtt- 
rocka)- and in 1881 Collett described as Scandinavian 
Lilljeborg’s svartbuksrocka (R. nidrosiensis). All these 
forms unquestionably belong to the Scandinavian fauna; 
but Collett further established in 1878 another species, 
Raja hyperborea, to which the said fauna can probably 
lay claim. These species may be distinguished as follows: 
A: Blunt-snouted. Internasal width more than 
70 % of the distance between each nostril 
and the tip of the snout: — Raj* clavatse. 
a: Root of the aculei nail-headed. Distance 
between each nostril and the tip of the 
snout 15 % or less of the breadth of 
the disk Raja clavata. 
b: Root of the aculei grooved. Distance 
between each nostril and the tip of the 
snout at least 16 % of the breadth of 
the disk. 
a: Upper median line of the tail armed 
with a series of aculei. 
aa: Aculei in the median line of the 
back and tail at most about 16- . Raja radiata. 
bb: Aculei in the median line of the 
back and tail at least about 24__ Raja hyperborea. 
(3: Upper median line of the tail with- 
out aculei' Raja falsavela. 
B : Sharp-snouted. Internasal width less than 
70 % of the distance between each nostril 
and the tip of the snout: — Rajse lteves. 
a: Ventral side light, plain, without dark 
punctuation. 
a: Upper median line of the tail with- 
out aculei Raja fullonica. 
(3: Upper median line of the tail arm- 
ed with aculei _ Raja lintea. 
b: Ventral side dark or marked with small 
dark dots and streaks. 
a: Length of the snout less than 18 % 
of that of the body or than 28 % 
of the breadth of the disk Raja batis. 
(3: Length of the snout more than 18 % 
of that of the body o.r than 28 % 
of the breadth of the disk. 
aa: Aculei (even if small) at the 
eyes. Ventral side blackish and 
with indistinct punctuation Raja nidrosiensis. 
bb: No aculei at the eyes. Ventral 
side comparatively light and 
with distinct dots and streaks.- Raja oxyrliynchus. 
Scandinavian Fishes. 
139 
