
852 THE AMERICAN NATURALIST. . [Vor. XXXVI. 
Obviously if this portion of the spine had projected freely, and 
were not anchored by insertion in the soft parts, it would have 
been not only a useless appendage but a positive hindrance to 
the creature, besides being constantly exposed to injury; but 
if we conceive of it as inserted in the integument in the same 
manner as the anterior prolongation of Oracanthus vetustus,} 
its function as a defensive organ and as a support for the pos- 
terior spine is readily understood. Evidence that this was a 
paired spine, and therefore not occupying a position in the 
median line of the back or of the head, is afforded by the 
fact that the exposed face of the anterior branch is turned so 
as to present the denticles toward the left-hand side; and the 
organ may therefore be interpreted as a lateral head spine 
belonging to the left side of the body. 
The posterior spine is very similar to the single defenses of 
Physonemus, but is more strongly keeled and broader at the 
base. The distal half of the posterior margin bears a double 
row of closely set denticles resembling those of E. maccoyanus. 
The sides of the spine are occupied by numerous fine, smooth 
longitudinal costz, of which about fifteen are to be counted 
along the line where the cross section shown in the figure is 
taken. The intercostal spaces, more particularly in the basal 
portion of the spine, are studded with numerous small tubercles, 
which are stellate in the unworn condition, and vary in shape 
between conical and spiniform. In many cases their summits 
are mucronate with the points reflected toward the basal por- 
tion of the spine, and the resemblance of these tubercles to 
certain types of placoid scales is very marked. It is probable 
that the imperfect spine illustrated in Pl. XXII, Fig. 3, of the 
sixth volume of the Minois Paleontology, represents a young 
individual of this species. 
Genus Campodus de Koninck. 
This genus of cestraciont sharks is represented in the Coal 
Measures of North America by three species, one of which — 
C. variabilis (N. and W.)— is of importance as affording a 
. 1 6f. J. S. Newberry, Trans. N. Y. Acad. Sci., vol. xvi (1897), p. 287, Pl. XXIL 
Fig. 3. 
