468 PHANEROPLEURON ANDERSONI 
The length of body equals about 54 lengths of the head. It re- 
mains of tolerably equal thickness from the pectoral region to that 
of the ventral fins, and then gradually tapers off to a finely 
pointed caudal extremity, which is, usually, slightly bent upwards. 
When the mouth is shut, the head also presents a triangular con- 
tour, both its upper and its under outlines rapidly shelving towards 
the snout. 
The scales are exceedingly thin, and, apparently in consequence 
of containing very little bony matter, they are apt to run into 
one another and lose their distinctness when fossilized. But so far 
as the best preserved specimens enable me to judge, they were large 
and circular, and their outer surfaces were marked by very slight 
and delicate, granular, radiating stria, which may, however, be indi- 
cations of internal structure and not of ornamentation (PI. III. 
[Plate 35] fig. 7). These differences from the scales of Holoptychius 
become particularly obvious when, as in the slab in the British 
Museum above referred to, specimens of the two genera lie side 
by side in the same matrix, or when, as in fig. 3, Plate III. [Plate 35], 
detached scales of Hloloptychius have become imbedded in the midst 
of a specimen of Phaneropleuron. 
The cranial bones are smooth, or, at most, present irregular and 
scattered grooves. The cranium seems to have been much more 
compressed from side to side than in most Devonian fishes, but I can 
say little else respecting its structure, as it is much injured in all 
the specimens I have seen. In no specimen are the boundaries of 
the cranial bones defined. The operculum, however, is large. The 
orbit seems to have been situated far forwards, and the gape is 
long. Both the upper and the lower jaw are beset with a single 
series of sharp short conical teeth. One specimen on the slab 
21620 in the British Museum exhibits the only view of the under 
surface of the head I have met with, and proves that the jugular 
region was protected by bony plates. Whether there were more than 
the two principal ones, or not, however, I cannot make out with 
certainty. 
The pectoral arch is well developed, but I can say nothing as to its 
individual components, nor are the pectoral fins thoroughly well pre- 
served in any specimen. Such parts of them as exist lead me to the 
belief that they were shorter than the ventrals, but like them acutely 
lobate. 
No pelvic bones are discernible, but the ventral fins are beauti- 
fully displayed in two examples on the slab 26120 in the British 
