598 
Proceedings of the Royal Society 
anterior part of the trunk are higher than broad, a circumstance 
distinguishing it from all the other species of this genus. 
According to specimens exhibited by the author, the scales are of 
different forms on different parts of the body, being very minute, 
and nearly equilateral aloug the belly ; the fins are large, and the 
dorsal is placed so far back as to be nearly opposite the anal ; the 
interspinous bones of the azygos fins are well developed, and there 
are traces of vertebral apophyses, but none of vertebral bodies. On 
the top of the head are shown the parietal, mastoid, frontal, post- 
frontal, and prefrontal bones, with a single nasal forming a pro- 
jection above the mouth. On the side of the head, the operculum, 
suboperculum, superior maxillary bone and lower jaw are distinctly 
recognisable, with a large triangular plate, covering the cheek 
above the upper jaw bone, and smaller ossicles around the orbit, 
which is placed very far forwards. The broad superior maxillary 
bone is beveled off for the orbit in front, to a narrow point which 
comes in contact with a small intermaxillary situated below the 
nasal and prefrontal bones. The teeth are conical and of two sizes, 
large ones alternating with small. The branchiostegal apparatus 
consists of numerous narrow flattened plates, and the shoulder 
girdle shows the supra-scapular, scapular, and coracoid bones, with 
a triangular plate in front of the lower end of the coracoid, analogous 
to a similar plate in the recent Polypterus. 
A comparison was made between the osteology of the head in 
Pygopterus and in Amhlypterus, showing the very intimate corre- 
spondence in the form and arrangement of the bones in those two 
genera ; and the appearances in both were then compared with the 
structure of the skull in the recent Lepidosteus and Polypterus. 
The general structure of Eurynotus was then noticed, and several 
of its facial bones described, together with the peculiar rounded 
teeth with which the jaws and palate are furnished. The opercular 
apparatus and superior maxillary bone differ considerably in form 
from those in Amhlypterus, and still more marked is the difi'erence 
in the shape of the teeth ; but the two genera agree in the form and 
arrangement of the branchiostegal plates and in the general struc- 
ture of the fins and scales. A specimen in the St Andrews Museum, 
shows distinctly that there were two rows of fulcral scales along the 
anterior edge of the dorsal fin, at least of Eurynotus. 
