WEAKFISHES 
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in the size at which this change takes place. An examination of a number of regalis 
from Chesapeake Bay showed that the change to an emarginate condition takes 
place when the fish reaches a total length between 250 and 300 millimeters. All 
those below 250 millimeters have the middle rays of the caudal longest, in all those 
over 300 it is distinctly emarginate, while in those between these lengths both condi- 
tions may be found, and some of them have a caudal fin that can best be described 
as truncate. In arenarius, on the other hand, the middle rays of the fin are longest, 
even in specimens over 300 millimeters long. It may be remarked that the fins of 
these fishes are rather brittle, and in 
preserved material they are more or 
less frayed. This probably explains 
why this character is not mentioned 
more often in discussions of the dif- 
ferences between the two forms. 
However, judging from the condi- 
tion of our specimens, it is apparent 
that the difference in the form of the 
caudal is substantially as described. 
Number of gill rakers . — This 
character has been mentioned by 
previous writers as differentiating 
the Gulf and Atlantic forms, and 
the present study has shown it to 
be usable, but there is considerable 
overlapping. The modal number 
for regalis in specimens of over 70 
millimeters, standard length, is 
5 + 12, while in arenarius it is 3 + 10 
or 4 + 10. In the study of this 
character the size of the fish must 
be taken into consideration, since it 
has been found that the number 
varies with the size, especially in 
arenarius. In the young fish the 
gill rakers are comparatively longer 
and more slender. As the fish grow 
older they become shorter and 
stouter, and the foremost one on 
the lower limb of the first arch and 
one or two uppermost ones on the 
upper limb tend to become absorbed 
and disappear. Moreover, this 
disappearance is more marked in arenarius, and consequently when larger specimens 
are compared the difference is more pronounced. 
For the purposes of the present study all specimens have been divided into two 
groups, those of 70 millimeters or less and those over 70 millimeters standard length, 
and like groups have been compared. It might have been desirable to make a finer 
division of groups, but thcre^was not enough material of all sizes in both forms. 
However, this division seems sufficient to bring out the essential facts. Figures, 1 and 
56401—29 2 
10 II IZ 13 
NUMBER OF GILL RAKERS ON LOWER LIMB OF 
FIRST ARCH. 
Figure 2. — Frequency distribution of the number of gill rakers on 
the lower limb of the first arch of Cynoscion arenarius and C. regalis. 
The one gill raker that stands at the angle of the arch and has one 
root on the lower limb and one on the upper limb has been included 
uniformly in this count 
