372 Mr. T. Atthey on Pteroplax cornuta. 



attached. Beliind these projections the borders of the post- 

 orbitals, as they go to join the squamous, are concave. 



The squamous, a little larger than the last, are four-sided : 

 the extei'nal side is convex, longer than the others, and the. 

 upper surface is convex like that of the postorbitals ; these 

 bones join in front with the last named, internally with the 

 parietals, and behind with the epiotics. The surface-pitting 

 is much less strongly marked on the squamous than on the 

 two bones in front of them. 



Tlie supraternj^oralsj the jugals, and the quadrato-jugals are 

 not visible on the upper surface of either of our specimens. 



The epiotics cojnplete the ring of bones around the sides of 

 the parietals, and form the posterior external angles of the 

 cranium ; these angles are produced backwards, in a conspi- 

 cuous and remarkable manner, into what have been called 

 horns, whence Pteroplax has received its specific name cornuta. 

 The parts of the skull from which these horns project are thick 

 and strong, standing up in a ridge, which from above the base 

 of the horn passes forwards and then, curving inwards, is 

 merged into the upper surface of the occiput, its external side 

 gradually subsiding to the level of the other bones. 



The epiotics are narrow bones wedged in, as it were, be- 

 tween the so-called supraoccipitals and the squamous and 

 reaching the parietals ; they also form a portion of the occi- 

 pital surface, and "w ith it and their horns give attachment to 

 muscles stretching down the neck. 



The so-called supraoccipitals or superior occipitals are rather 

 narrow, elongated transversely, joining each other on the 

 median line, and, hemmed in by the epiotics^ overhang the 

 occipital surface ; their external posterior angles are more 

 or less acute ; below they articulate with the exoccipitals and 

 the quadrates. 



The occipital surface, concave vertically, is much arched 

 from side to side, owing greatly to the epiotic horns, and 

 presents the same slightly overhanging border that we see in 

 the other two Labyrinthodonts of this district. Three occi- 

 pital protuberances exist, one at the upper margin, another 

 near to or at the base of the skull, the third, which is small, 

 just below the first. These are bisected by the median suture. 

 From a little distance on each side of these projections the 

 vertical concavity of the surface is divided by a rather rough 

 ridge into an upper and a lower groove ; and in each runs a 

 delicate rather obscure suture ; the upper unites the so-called 

 supraoccipitals to the exoccipitals, the lower these latter bones 

 to the quadrates. 



The true occipital is undistinguishable, and the basioccipital 



