1862.] HUXLEY — CARBONIFEROUS LABYRINTHODONT. 65 



lated with its upper half, in which case the distance (a, b) on the 

 rib would be practically equal to the excess of length of the upper 

 division of the transverse process over that of the lower. 



The skull, a dorsal vertebra, and a rib of Anthracosaurus being 

 known, I now return to the question, what are the affinities of that 

 Labyrinthodont ? 



The large size of the teeth, the comparative solidity of their bases, 

 and the complex character of the labyrinthic ramifications of the pulp- 

 cavity are all characters in which Anthracosaurus resembles the 

 Mastodonsaurus of von Meyer and Plieninger and its allies, and differs 

 from Archegosaurus. Whether Anthracosaurus had well-ossified occi- 

 pital condyles like Mastodonsaurus, or cartilaginous ones such as 

 were probably possessed by Archegosaurus, does not appear, the 

 fossil being defective in this region. In the large size of the an- 

 terior palatine foramina, the extent to which the palate-bones are 

 united with the maxillaries, in the form of the pterygoidean arch 

 and that of the basisphenoid, Anthracosaurus is nearer to Archego- 

 saurus and Dasyceps than to Mastodonsaurus. 



But the vertebrae are altogether Mastodonsaurian. The vertebras 

 of Mastodonsaurus were described and figured in 1844 in the well- 

 known work of von Meyer and Plieninger, ' Beitriige zur Palaonto- 

 logie Wiirtembergs.' No fewer than seventeen vertebras were dis- 

 covered in one slab, together with the skull of this remarkable 

 Labyrinthodont ; another block contained eight vertebrae, belonging 

 to the same animal, but not immediately succeeding the former ; and 

 a third slab of stone contained five more trunk-vertebrae, besides 

 three others which were caudal. Dr. Plieninger seems inclined to 

 think that all these cervico- dorsal vertebrae belonged to one animal : 

 but even the fact that seventeen vertebrae were found together in one 

 block, and the existence of caudal vertebrae, must be amply sufficient 

 to satisfy every anatomist of the untenability of the hypothesis that 

 the Labyrinthodonts were frog-like or toad-like in form. 



The trunk- vertebrae of Mastodonsaurus are biconcave, and much 

 flattened from before backwards. The neural arch ends above in a 

 strong spinous process ; there are well- developed zygapophyses, and 

 the stout transverse processes exhibit a division into an upper longer 

 and a lower shorter portion. So far they are very similar to those 

 of Anthracosaurus. The ribs again are strikingly similar to those 

 of Anthracosaurus, as may be seen by comparing plate 5. figs. 1 & 2 

 of the work cited with fig. 2, B. 



On the other hand, the vertebrae of Mastodonsaurus, according to 

 Plieninger, presented characters which I do not meet with in An- 

 thracosaurus. Thus, the articular surfaces of the bodies of the vertebrae 

 of the Triassic Amphibian are inclined towards one another superiorly, 

 while those of Anthracosaurus are parallel ; and the upper and lower 

 portions of the transverse process, which are said by Plieninger to be 

 separated by a suture, so that the neural arch, with the upper longer 

 transverse processes, readily separates itself from the body with the 

 lower and shorter transverse processes, are, so far as I can observe, 

 perfectly continuous in the Carboniferous Amphibian. 



VOL. XIX. PART I. F 



