36 PALEOZOIC FISHES OF NORTH AMERICA. 
denticulation of both sides of the pointed extremity show distinctly that 
they have only a superficial resemblance to the defensive spines of Elas- 
mobranch fishes. When complete and seen in position they reveal their 
affinities with the lateral cornua of the cephalic buckler of Cephalaspis. 
The external surface of the plates to which these spines are attached is 
marked with a conspicuous and peculiar ornamentation, much like that of 
Bothriolepis ; a series of convoluted, locally parallel, raised and beaded 
lines. As the central plates of Acanthaspis have never been found in con- 
nection, it is impossible to give at present the form of the cranium, but 
they are seen to be in pairs, and it is highly probable that when united 
they formed a rounded head-buckler, which differed from that of Cepha- 
laspis mainly in being composed of a series of separable plates, instead of 
forming a solid box. 
ACANTHASPIS ARMATUS Newb. 
Plate XXX, Figs. 1-4. 
Cranium consisting of a number of bony plates, forming several pairs, 
and differing considerably in outline. To at least one of these pairs are 
attached, on the outer margin, strong, slightly curved, carinated, tuber- 
culated and toothed spines. The external surface of the plates is covered 
with convoluted or radiated raised lines, which are more or less tuber- 
culated. 
Several cranial plates of this species are represented in the figures now 
published, and these will give a better idea of their form and markings than 
any verbal description can do. These plates, and the spines which are con- 
nected with some of them, are frequently met with in the Corniferous lime- 
stone of Sandusky and Delaware, Ohio, but like the cranial plates of Ony- 
chodus, they seem to have had no bony attachment to each other, and in the 
dissolution of the body of the fish which bore them they have been widely 
separated. There is little doubt that sooner or later some cranium will be 
found in which the bones hold their normal positions, and from such a spec- 
imen a more complete description of the fish can be drawn than can now be 
given. Waiting the discovery of such complete material, the plates now 
