1186 
SCANDINAVIAN FISHES. 
back in the young 0 . The length of the tin is about 
9V 2 — 12 % of that of the body. The second dorsal is 
considerably higher (sometimes twice as high or a little 
more), but essentially of the same form, its length 
varying between about 18 and 26 % of that of the 
body, with the highest percentage in old specimens. 
Behind it meets the caudal tin, or overlaps the upper 
anterior margin thereof, but is always sharply defined, 
as well as the first dorsal, at its posterior termination. 
In front it is separated from the first dorsal by an in- 
terval which in adult specimens (over 2 1 / 2 dm. long) 
varies with age from about 6 to 4 % of the length of 
the body, and which, according to Wilder’s measure- 
ments of the North American fresh-water form, is less 
in the males than in the females. The diphycercal 
(almost symmetrical) caudal fin is uniformly widened 
behind (tongue-shaped), with short, triangular but- 
rounded tip. The entire length of the caudal fin oc- 
cupies in adult Lampreys about 9V 2 — 8 V 3 % of the 
length of the body. 
The anal aperture lies below the anterior portion 
of the second dorsal fin, at a distance from the tip of 
the snout measuring 75 b — 72 % of the length of the 
body, further back in the young than in the old. The 
urogenital papilla is comparatively small. As men- 
tioned above, all the Cyclostoines are without anal fin; 
but between the vent and the caudal fin a dermal carina 
frequently occurs, similar to that of the dorsal margin. 
The coloration varies with age, locality, and the 
time of year. Our figure represents a nearly ripe fe- 
male in a fresh condition, as received by the Royal 
Museum from Ringkjobing (Jutland) at the end of May 
through Mr. 0. Fredericksen. Here only the white 
and blue colours prevailed, the former being pure on 
the belly, the latter pale but unmixed on the head, and 
composing the pale ground-colour of the sides and back, 
which were mottled with a darker blue, shading into black. 
The fins were pale, mottled with blue, with a dash of gray. 
The pupil was black, the iris of a faint silvery lustre 
but not much paler than the prevailing colour. The 
gill-openings and mouth were tinged with red. Dono- 
van" figures and describes the species as more varie- 
gated, with a ground-colour of lustrous green, mingled 
with blue, yellow, and red, with a handsome marbling 
of black. He also adduces blue and olive varieties, as 
well as reddish ones mottled with chestnut-brown in- 
stead of black. According to Kroyer the under surface 
of the head is yellow, the fins being reddish, of a dark 
orange, the dorsal fins besides mottled with black. Ac- 
cording to both Malm and Collett the marbling is 
absent in young specimens; and according to Lesueur 
and Dekay this also applies to the larva?. 
The larval stage, so far as is known, has not yet 
been observed in Europe; but in North America an 
Ammocoetes bicolor was described by Lesueur (1818) 
and another form, Amur, unicolor , by Dekay (1842), both 
of which have been referred by Jordan and Fordice to 
Petromyzon marinus as its larva?. The former of these, 
according to Dekay, has not been rediscovered since 
Lesueur’s time, but had been named from its colora- 
tion, reddish on the back and sides, white on the belly, 
with a sharp, undulating limit between these two co- 
lours. The latter ( unicolor ) is in all respects still more 
like an earthworm, but has developed distinct eyes. Its 
coloration is described by Dekay as a nearly uniform 
dark or dusky brown, occasionally verging to bluish, 
somewhat lighter beneath; the anterior part of the head 
darkest. The form of the body cylindrical for two 
thirds of its length from the head, becoming slightly 
'compressed just anterior to the vent, very much com- 
pressed and acuminated at the tail. Greatest depth of 
the body 7 1 /' 2 % of its length. Surface smooth, with 
between 80 and 90 transverse folds (myocommata), 
giving the body an annulated appearance. The fins ap- 
pear to be nothing more than mere membranous pro- 
longations of the skin, without the slightest vestige of 
rays. The dorsal commences at the beginning of the 
3rd fifth of the length of the body (from the snout), in 
a scarcely perceptible furrow, and advances low and 
subequally until about the middle of its length, when 
it begins to rise, and then rapidly diminishes at the tip 
of the tail, where it unites with the caudal and anal, 
which latter is obsoletely triangular, and becomes in- 
sensibly effaced at a point corresponding to the begin- 
ning of the last fourth of the length of the body. The 
vent is a large longitudinal aperture between the 2nd 
a Our measurements of Sea Lampreys 2 1 / 2 — 8 1 / dm. long show that the distance from the tip of the snout to the beginning of the 
first dorsal fin diminishes with increasing age from 53 to 48 % of the length of the body. Kroyer’s measurements of specimens 4 — 8 f'.j 
dm. long indicate that these percentages decrease from 51 'A to 50. 
b According to Meek (1. c.) exceptionally 77 or even 80. 
c Brit . Fish., pi. LXXXI. 
