from the Shales of the Northumberland Coal-field. 275 



equally large Labyrinthodont, differs considerably from those 

 just described. It is not quite four inches long, and near to 

 the proximal end it is upwards of half an inch wide ; the sides 

 are flattened from before backwards, and exhibit a wide shal- 

 low groove from one end to the other. The tuberculum is 

 scarcely distinguishable from the capitulum, except by its 

 projecting boldly outward from the convex margin of the rib ; 

 its articular surface is continuous with that of the capitulum, 

 forming with it a wide diagonal termination. Thence the rib 

 tapers rather rapidly to the distal extremity, which is a little 

 recurved. 



Two or three limb-bones have likewise been found, which, 

 from their size, probably belonged to this species. One of 

 these, apparently a femur, is an inch and a half in length and 

 iive-eighths of an inch wide at the middle of the shaft, which is 

 much compressed from front to back, and is a little arched in 

 the same direction ; there is a longitudinal depression extend- 

 ing from end to end. The extremities are much expanded, 

 and they both appear to have double articular surfaces ; that 

 which is assumed to be the distal extremity is more expanded 

 on one side than on the other. 



From the shortness of this bone it would seem that the 

 limbs of this animal were but feebly developed in comparison 

 with the size of the body. 



In concluding this description of the remains of this fine 

 large Labyrinthodont reptile, a few words may be desirable on 

 its relationship with the generic forms previously known. It 

 has been already stated that it is closely allied to Loxomma^ 

 with which it agrees in having large and probably oblique 

 eyes, placed near together and in a backward position. It 

 agrees pretty well, too, with it in the general form of that 

 assemblage of bones which we have called the cranial shield, 

 though the curves are more flowing. But the parietals differ 

 considerably in shape : in Loxomma they appear to be simply 

 elongated, and scarcely, if at all, enlarged behind * ; while 

 in Ptero])lax they are much enlarged posteriorly, and the 

 frontals seem to be more produced. The sternal plates like- 

 wise differ from those of Prof. Huxley's genus, in which 

 the lateral ones are quite short ; but in Pteroplax they are 

 much elongated, agreeing in this respect with Archegosaurus ; 

 and the central plate in Loxomma is devoid of the remarkable 

 lateral lobes which characterize that of our genus. 



We have also seen that this new reptile resembles to some 

 extent Dasyceps, particularly in the two occipital horns ; but 

 the small eyes, backward position of the parietal foramen and 

 * Proc. Geol. Soc. vol. xviii. p. 292, pi. 11. 



