I] 
The Ide is one of the larger species within this 
genus. According to the reports sent in to the Swedish 
Fisheries Committee of 1881, it attains in Sweden a 
length of about 9 dm. and a weight of 6 4 / 5 kgra. These 
statements, however, undoubtedly refer to exceptions, 
unless they are exaggerated, or perhaps depend on a, 
confusion of this species with the Asp ( Aspius rap ax). 
The ordinary length of the Ide in an adult state is 
about 3 or 4 dm. At a length of 5 dm. it weighs 
at most from 2 to 2 ’/a kgm. 
The body is moderately compressed or even rather 
bulky. The greatest depth, which lies just in front of 
the beginning of the dorsal hn, usually measures in 
young specimens rather more than 1 / 5 , in old 25 — 30 %, 
of the length of the body, and the greatest breadth or 
thickness is not quite half the depth. The latter measure- 
ment varies, however, according to sex, age, or season, 
in young specimens being sometimes only about 2 / 6 of 
the depth, and rising in old specimens to about 45 — 
51 % thereof. The least depth of the body is in young 
specimens about 10 % (9V 2 ° /o \ in old about 11 %, of 
its length. The back, which is fairly broad and convex, 
and which rises more or less abruptly, according to the 
fatness of the fish, from the occiput, forms a slight 
upward curve. The belly from the isthmus to the vent 
is fairly straight, except during the spawning-season, 
when it forms in the female a downward curve, be- 
ginning at the chin. Between the pectoral and ventral 
lins the belly is flat, but subsequently, between the 
latter and the vent, becomes convex and somewhat 
carinated. 
The length of the head usually occupies in mode- 
rate-sized specimens a little more than J / 5 (22V 2 — 21 1 / 2 %) 
of that of the body. In old specimens this proportion 
is almost exactly 1 f., and in young ones the head is 
as usual larger in comparison with the rest of the body. 
The front part of the head is broad and convex, forming 
a gradual curve from the snout to a point somewhat 
in front of the nostrils, where it is slightly depressed". 
The breadth of the interorbital space increases, even 
relatively, with age from a little more 6 than 37 % to 
nearly 46 % of the length of the head, the latter in 
specimens 4 or 5 dm. long. As a rule, however, this 
breadth is less than 3 / 4 of the base of the dorsal fin, 
and we have never found it to exceed 85 % thereof. 
765 
The sides of the head are. somewhat compressed and 
flattened. The snout is blunt, broad, and only slightly 
projecting, the margin of the upper jaw (middle of the 
intermaxillaries) being the most prominent point. The 
mouth is small and turned slightly upwards. In full- 
grown specimens the corners of the mouth do not ex- 
tend behind the perpendicular from the middle point 
between the eye and the nostrils, while in young spe- 
cimens they reach comparatively a little further back, 
or to a line with the anterior margin of the eye. The 
length both of the snout and the upper jaw increases, 
even comparatively, with age, most, however, in the 
former case; the length of the snout increasing in spe- 
cimens 8 — 42 cm. long from about 27 to 34 % of the 
length of the head, and that of the upper jaw from 
about 27 to 31 % of the same. A retrogression to the 
characters of youth may sometimes be found, however, 
in old specimens. When the mouth is opened, the 
upper jaw is slightly protruded. The length of the 
lower jaw measures about 36—40 % of that of the head. 
The longitudinal diameter of the eyes decreases compa- 
ratively, during growth, in the above-mentioned speci- 
mens, from about 30 to 15 % of the length of the head, 
i. e. from a little less than the breadth of the inter- 
orbital space to only V 3 thereof. At the same time 
the postorbital length of the head increases from some- 
what less than 1 / 2 to about 56 % of its entire length. 
The nostrils are set, as usual in the genus, close to 
each other and nearer to the eye than to the tip of the 
snout, the narrow partition-wall between them being 
elevated into a kind of lobe. The anterior nostril is 
round, the posterior crescent-shaped and larger. The 
distance between the two anterior nostrils is about half 
the breadth of the interorbital space. As usual in the 
genus, the head is scaleless, and is covered on the sides 
with a thin, transparent skin, through which the oper- 
cular and facial bones are distinctly visible. The occiput 
and forehead, on the other hand, are clothed with a 
thicker, firmer, and richly muciferous skin, which has 
a smooth and even surface. The branchiostegal mem- 
brane extends behind the gill-cover in a broad rim; 
its three rays are flat, broad, and curved; and below, 
as is usually the case in the genus, it is united to the 
isthmus, in a line with the hind margin of the pre- 
operculum. Idle pseudobranchiae are well-developed. 
a With regard to this depression see above, p. 716, rote a. 
b In exceptional cases a little less. 
