178 MR. T. ATTHEY ON PTEROPLAX COENUTA. 



inches and nine-tenths, between the posterior ends of the orbital 

 curves two inches and a half, between the anterior ends of the 

 same one inch, over the anterior broken ends of the frontals 

 rather more than one inch. 



Tlie pitted sculpturing is iiTCgularly disposed over the suiiace, 

 the pits vaiying much in form, size, and depth, being on the 

 whole smaller and less deep than those of the crania of Loxomma 

 and Anthracosaurus ; on the parietal bones they are prolonged 

 into grooves radiating from the centres of ossification on each 

 side of the parietal foramen. The pits are most strongly marked 

 on the postfrontals and postorbitals, and are largest and groove- 

 like on the frontals. On these bones there is besides a channel 

 or groove at each margin, studded with pits, probably a mucus- 

 groove. The pits on the frontals are all inclined forwards, and 

 look as if they served to lodge blood-vessels. None of the small 

 punctures which exist at the bottom of the pits in Loxomma are 

 visible in the pits of Pteroplax, any more than in those of Anth- 

 racosaurus. 



The orbits appeal' to have been large for the size of the skull ; 

 their internal, concave, osseous margins, formed of the postfi'ontal 

 and postorbital bones, alone remain to testify to this. They are 

 placed where the skull rapidly tapers to the elongated frontal 

 region. The rest of their outline was probably partly membran- 

 ous or ligamentous and cartilaginous. 



The prolonged and narrow anterior end of our specimen ter- 

 minates abruptly at a somewhat oblique transversely fractured 

 surface. 



The frontal hones constitute nearly the wliolc of this narrow 

 part of the skull, which appears slightly deviated from the straight 

 line, as if it had received after death a blow on the left side of 

 the anteiior end, which had started the posterior end somewhat 

 from its articulation with the parietal bones. This part is rather 

 ])roadcr at its distal end than elsewhere. 



The frontals arc united to each otlier on the median line ; be- 

 hind, and at each side of that line, they form together a retreat- 

 ing angle, into wlii( h are received tlie united ends of the parietals ; 



