100 PALEOZOIC FISHES OF NORTH AMERICA. 
stone; O. Ortoni, from the Huron shale; and 0. Hopkinsi, from the Che- 
mung. They were all apparently marine, cycliferous Ganoids of large 
size, probably Crossopterygians, of which the head was covered with a large 
number of enameled plates ornamented with appressed double cones of 
enamel, and forming a tessellated pattern most like that of Polypierus. The 
bones of the head seem to have disarticulated readily, for they are always 
found separated and generally scattered. The cranial structure has never 
been fully illustrated, but the jaws, teeth, and scales are described and fig- 
ured in the first volume of the Palaeontology of Ohio 
It may be remarked in this connection that in the genus Aspidorhynchus 
a detached triangular bone is set in or on the symphysis of the mandibles, 
serving to complete the arch of the jaw and protect it from rupture. 
Ho.oprycuHius ? PUSTULOSUS, 0. sp. 
Plate XX, Figs. 11, 11%. 
In the Chemung group at Warren, Pa., occur many large, thick, bony 
scales, of which the generic relations must remain doubtful until more ma- 
terial shall be obtained. These scales are round, ovoid, or elliptical in 
outline, the largest two inches in the longest diameter, one and a half inches 
in the shortest. The central portion of the exterior surface carries a con- 
siderable number of relatively large, round, scattered tubercles; the mar- 
gins being plain and smooth. By these characters they will be recognized 
wherever found, and doubtless in time much more will be known about the 
fishes which bore them. The specimens now in my hands I owe to the 
courtesy of Mr. C. E. Beecher, who collected them at Warren, Pa. 
HoLoprTycHIUS GRANULATUS, 0. sp. 
Plate XX, Fig. 9. 
Scales circular or elliptical in outline, one and a half inches in greater 
diameter; covered portion smooth; exposed portion closely set with fine 
rounded granules of enamel, which on the posterior margin are arranged in 
parallel rows; in the center and on the sides are promiscuously aggregated. 
These scales are not unfrequently found in the Chemung of northern 
