LABYRINTHODONTIA. 215 



exhibited in the large atlas of the toad. The body of the 

 vertebra agrees with that of the L. leptognatJms. The humerus 

 is regularly convex at the proximal extremity. A portion 

 of a somewhat shorter and flatter bone is bent at a subacute 

 angle with the distal extremity, and resembles most nearly 

 the anchylosed radius and ulna of the Batrachia. 



The femur has a subtrihedral and slightly bent shaft, its 

 walls are thin and compact, including a large medullary 

 cavity. The tibiae exhibit that remarkable compression of 

 their distal portion which characterizes the corresponding 

 bone in the Batrachia ; they likewise have the longitudinal 

 impression along the middle of the flattened surface. The 

 characters of the above-defined Labyrinthodont appear to be of 

 subgeneric value, which is indicated by the term Rhomhopholis. 

 Corresponding differences in the forms and proportions of the 

 skull, and in the form and relative position of the orbits, of 

 specimens tha,t have been discovered subsequently in the 

 triassic sandstones of Germany, have been similarly interpreted. 



In the Ldbyrinthoclon (Mastodonsaurus) Jaegeri — the 

 largest of the species. The skull, discovered in the lower 

 Keuper of Wurtemberg, is triangular, the two condyles pro- 

 jecting from the middle of the base ; the sides are straight, 

 and converge to the obtuse apex. The orbits are oval, 

 narrowest anteriorly, and are situated nearly midway between 

 the fore and back part of the skull. The nostrils are very 

 small, and are as wide apart as the orbits. 



Labyrinthodon (Trematosaurus) Braunii, Von Meyer. — 

 The genus was founded on a skull discovered in the bunter- 

 sandstein of Bernbourg. It is about one foot long, and, rela- 

 tively to its basal breadth, longer and narrower than in L. 

 Jaegeri, the sides converging at a more acute angle. The 

 orbits are elliptical, situated in the middle of the v skull, and 

 wider apart than in L. Jaegeri ; the nostrils are relatively 

 nearer together than in that species. There are a pair of pre- 



