978 
SCANDINAVIAN FISHES. 
Subgenus ALOSA. 
Sides of the body marked , at least in front , with dark spots. Lower anterior surface of the operculum coursed 
by more or less distinct grooves and ridges. Dorsal fin set so far forward that the distance between it and the 
tip of thj, snout is less than four times the postorbital length of the head. Inner part of the caudal lobes fur- 
nished with foliate scales , larger than the others. 
Now that all attempts to employ the dentition as 
a means of defining subgenera within the genus Clupea 
have proved futile, no better prospect of attaining this 
object is offered, it appears, than by the different de- 
velopment and position of the fins. But the subgenus 
Alosa, which is further distinguished by the extremely 
feeble dentition of the mouth, is so well defined within 
the Scandinavian fauna that no difficulties meet us here 
in its characterization. In exotic forms, however, as 
a b 
Fig. 245. Scales from the left side of a Pilchard 20 cm. long (a) 
and from a ■ Shad 30 cm. in length ( b ). X 3. 
for instance in the Japanese Clupea zunasi , the striation 
of the opercula is hardly perceptible, and the lateral 
markings of the body are confined to a single small 
spot on the adipose membrane of the upper scapular 
region; and in the Mediterranean Clupea aurita, where 
the dark markings are also restricted to the upper part 
of the tract round the gill-openings, the said striation 
consists merely of a ridge crossing the anterior part of 
the operculum in an obliquely downward direction. But 
the other characters given in the above diagnosis range 
these forms beside our Shads, which may be regarded 
as the type of the subgenus, and which are usually to 
be recognised at the first glance by the striation of the 
opercula and the spots on the sides of the body, though 
the latter vary both in size and distinctness, being in 
some individuals wanting. 
The scales of this subgenus are more strongly 
developed at the basal angles of the fins and their bases 
than is the case in the preceding members of the genus. 
The caudal fin is covered to a great extent with scales, 
and bears on each side two patches of these, one on 
the upper and one on the lower lobe, among which the 
hindmost is the largest, and is also 'venous. Sometimes, 
however, these patches of scales are so thin and trans- 
parent that they easily escape observation. At the base 
of the dorsal fin, the upper angle of the pectoral fin, 
and fhe outer angle of the ventral fin, we find pointed 
scales, which partially conceal these fins; and rounded 
scales overlap the loiver margin of the pectoral fins, 
covering the lowest rays, while the base of the anal 
fins is also scale-clad. In texture too the scales of 
this subgenus differ from those of the preceding one, 
the radiating grooves, which are there extremely faint 
streaks (see above, p. 957), being here far more sharply 
defined (-fig. 245). 
Both the anal and the dorsal fins show a more 
pointed prolongation of the outer posterior corner than 
in the preceding subgenus. 
The most constant character, hoAvever, is the for- 
ward position of the dorsal fin, a character which is 
expressed in the above diagnosis of the subgenus by a 
comparison with the postorbital length of the head. 
This last measurement is relatively greater in the Shads 
than in the true Herrings, the validity of the character 
being thus unimpaired even when the trunk is shor- 
tened, as in the American Menhaden, which would else 
be referred by the position of the dorsal fin to the- 
preceding subgenus. 
