240 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Specimens. 
Dorsal 
scutes. 
Lateral 
scutes. 
Ventral 
scutes. 
Pectoral. 
Ventral. 
Anal. 
Caudal. 
Total 
length. 
Remarks. 
M. 
10 
90 
2. 085 
in Cope's Coll 
Xo. 11. A. sturio 
11 
g8 
3Ct 
35 
26 
26 
90 
.49 
Delaware City. 
No. 12. A. brevirostris.. 
12 
7 
31 
17 
19 
.54 
Do. 
No. 13. A. brevirostris . . 
11 
§7 
8 
8 
30 
20 
60 
.46 
Do. 
(91) 10 
7 
.58 
Do. 
11 
% 
.56 
Do. 
No. 16. A. brevirostris . . 
11 
if 
8 
31 
21 
22 
60 
.812 
Mus. Acad. Nat. 
Sci., Phila. 
Frequently the last dorsal scute, just in front of the dorsal fin, is divided in the ||i 
median line as indicated in the formula of the dorsal scutes of T^o. 14, or, there may || 
be two small scutes partially intercalated between the tenth and eleventh dorsal on ’ 
either side of the median line. j|' 
The contrasts between the dermal armature of the dorsal, lateral, and ventral ||| 
rows of plates is sufficiently well marked to constitute a good specific mark of dis- ^ | 
tinction; but these are not the only diiferences which the integuments of the two 'ji 
species present when compared together. ^ | 
In the young of A. sttirio, the most deeply pigmented portion of the integument lies ‘ | 
above the lateral row of scutes, while the abdomen presents almost a silvery white i jj 
tint. In the adult, on the other hand, the pigment is extended somewhat farther || 
down the sides and becomes different in color; so that instead of being greenish- 
brown, as in the young, there is a more decided greenish or olive tint observable over 
the back and sides. 
The skin of A. brevirostris in specimens up to nearly 2 feet in length is nearly 
smooth, in a fresh specimen, between the dorsal, lateral, and ventral rows of scutes, ' 
and of a richer and darker brown than in A. sturio. ' 
In the young of a A. sUirio, on the other hand, the skin in the same region is 
beset with minute, retrorse, dermal denticles, having an acuminate tip and a flat ex- 
panded base embedded in the integument. There can be little doubt that the sharp 
tips of these denticles represent, in part- at least, the enamel caps of the dermal 
denticles of other fishes, while the expanded flat bases represent the cementum plates 
of such teeth. 
As the animal becomes adult the well-marked roughness or shagreen-like feel of the 
skin in A. sturio, becomes less marked; the fine points or denticles projecting above the 
general level of the integument are no longer observable unless one exerts some pres- 
sure upon the skin, especially along the sides and ventral surface. The small, isolated 
denticles, with their circular basal plates, as seen in the young of A. sturio, are 
replaced in the adult by small lozenge shaped integumentary ossifications standing in 
oblique rows between the dorsal and lateral rows of scutes. The edges of these loz- 
enge-shaped pieces approximate each other much more closely than do the edges of 
the basal plates of the small integumentary denticles of the young. It is also clear 
that these latter stand in a genetic relation to the lozenge-shaped plates on the sides 
of the body of the adult sturgeon; that the basal plates of a number of the small der- 
mal denticles of the young have fused together by their edges to form the larger 
