986 
SCANDINAVIAN FISHES. 
with the posterior margin of the eyes, the length of 
the cheek behind them being less than its height below 
the eyes. The length of the lower jaw is 14 — 13 % 
of that of the body" or about 62 — 58 % of that of the 
head. The height of the dental part is less than in 
the Herring, measuring about 1 / 3 of the length of the 
lower jaw. At the symphysis the lower jaw is most 
like that of the Pilchard and only slightly prominent; 
but in old or lean specimens the symphysis is more 
truncate (deeper), and has two pairs of comparatively 
small chin-protuberances above. The jaw-teeth dis- 
appear more or less completely with age, most in the 
Allice Shad; but even in old specimens a fairly regular 
row may be found on the intermaxi llaries, a tooth or 
two in the front of the lower jaw, and traces of the 
dentiform crenelation on the hind part of the maxil- 
laries. There are no other teeth in the mouth. The 
differences in the gill-rakers of the two varieties have 
been mentioned above, and may be seen in the figures, 
flie opercular apparatus differs from that of the Her- 
ring in the greater extension of the preoperculum back- 
wards and downwards and in a corresponding reduc- 
tion of the operculum below, the obliquely set inferior 
margin (the suture with the suboperculum), which is 
fairly straight or incurved, measuring only about 1 7 1 / 2 
— 21 % of the length of the head, 35 — 47 of that 
of the maxillaries, or 29 — 35 % of that of the lower 
jaw. An equally perceptible alteration of growth ap- 
pears in the form of the suboperculum, which becomes 
narrower, as a rule, during growth, its breadth at the 
middle decreasing from about 60 to 40 % of the length 
of the said suture. As the length of the body increas- 
es from 12 to 40 cm., the postorbital length of the 
head rises from about 45 '/ 2 to 58 % of the entire 
length thereof, or from about 25 1 / g to 30 % of the 
distance between the dorsal tin and the articular knobs 
of the maxillaries. When the postorbital length is 
measured in an oblique direction (to the lower posterior 
angle of the operculum), these percentages increase re- 
spectively from about 52 V 2 to 62 V 2 and from 29 V 2 to 32. 
The length of the pectoral tins, which are oblique- 
ly pointed, is about 16 — 14 %, that of the ventral 
tins about 10V 2 — 8V 2 %■> of the length of the body. 
The preabdominal length varies between about 22 and 
26 %, the postabdominal between 21 and 24 Vs of 
the length of the body. 
The dorsal tin begins at a distance from the ar- 
ticular knobs of the maxillaries measuring about 42 — 
44V 2 % °f the length of the body, or 90 — 99 % of the 
distance between the ventral tins and the same points. 
Its height decreases with age from about 15 to 11 % c , 
and the length of its base varies between about 13 
and 15 %>, of the length of the body, the latter propor- 
tion seeming as a rule to be somewhat less in young 
specimens than the former, greater in old. The caudal 
tin is deeply forked, the middle rays measuring only 
V 4 — V 5 of the length of the longest ones, which varies 
between about 2 2 x / 2 and 19 % of that of the body. 
The inferior lobe of the caudal tin is, as usual, some- 
what longer than the superior. 
The anal tin is of special interest from a syste- 
matic point of view. The form is indeed highly vari- 
able, but we have failed to discover any rule for its 
variations. Sometimes the tin is comparatively high, 
the length of its longest ray measuring as much as 
2 / 5 of its base. In other specimens it is as low as in 
the preceding Clupeoids, the height being but little 
more than V 4 of the base. But the extent of the tin, 
the length of its base, seems to afford a distinction 
both between the sexes and the varieties. In each 
variety of the Shad, so far as our observations have 
been carried, the females have a, comparatively longer 
anal tin than the males; and the base of the anal tin 
is comparatively longer in the Allice Shad than in the 
Twaite Shad. We may here adduce the following ex- 
amples of the rule: 
“ It sinks in the oldest Shads to 12 % thereof, judging by a stuffed specimen. 
b About 55 — 58 % in the Pilchard. 
c Or even to 9 °/, judging by a stuffed specimen. 
