48 



ERITISIT FOSSILS. 



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 strige, which may, however, be indica- 

 tions of internal structure and not of ornamentation (PI. III. 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. detached scales of Holoptychius 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 com- 

 pressed from side to side than in most Devonian fishes, but I can say 

 little else respecting its structuie, 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 pro- 

 tected 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 

 preserved 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 beautifully 

 displayed in two examples on the slab 26120 in the British Museum, 

 and in another specimen marked 26117 in the same collection. 



Their length exceeds the greatest vertical diameter of the body. A 

 taper central lobe extends through the whole length of the fin, ending 

 in a point at its fine end. It is covered throughout with cycloid scales, 

 having the same characters as those of the body, and both edges are 

 fringed with delicate fin-rays. 



The notochord was persistent throughout the whole length of the 

 vertebral column, while the superior and inferior arches were well 

 developed and thoroughly ossified. 



The neural spines are long, and are curved, so as to be somewhat 

 concave forwards and upwards. In the posterior moiety of the 

 body, elongated interspinous bones, narrow in the middle and 



