1862.] HUXLEY CARBONIFEROUS LABYRLNTHODONT. 67 



At present we are acquainted with two apparently very distinct 

 types among the Labyrinthodonts — that of the Archegosauria (Ar- 

 chegosaurus),nt present known to occur only in the Carboniferous rocks, 

 and that of the Mastodonsauria (Mastodonsaurus, Labyrinthodon, 

 Capitosaurus, Trematosaurus), which seem to have nourished in re- 

 markable abundance during the Triassic epoch. Both groups exhibit 

 the sculptured and polished* surface of the crania, the vomerine and 

 palatine teeth, the forwardly situated posterior nares, the permanently 

 distinct epiotic bones, the divided supra- occipital, the three sculp- 

 tured pectoral plates, the elongated, caudate, salamandroid body, and 

 the comparatively short limbs and weak feet which are distinctive 

 features of the Labyrinthodont Amphibia, as well as the more or less 

 complex ramifications of the pulp-cavities of the teeth, which they 

 share with Fishes and Ichthyosauria. 



But the Archegosauria have imperfectly ossified vertebral bodies t, 

 while the Mastodonsauria have them thoroughly well ossified, though 

 still biconcave ; and the Mastodonsauria have double ossified occipital 

 condyles, which have not been found in Archegosauria. 



Of the other distinctions, if such there were, of the two groups, 

 we know very little. It is true that the Archegosauria had, as von 

 Meyer has proved, in his splendid monograph ' Die Reptilien des 

 Steinkohls,' a persistent branchial apparatus and a very remarkable 

 scaly ventral armature. But what do we know with certainty about 

 the presence or absence of corresponding structures in the Triassic 

 Mastodonsauria''? Whatever may be the nature of the doubtful 

 Anisopus or Rhombopholis , it is certain that the African, probably 

 Triassic, Micropholis was protected by ventral scutes ; and until Mas- 

 todonsaurian Labyrinthodonts are found preserved as favourably as 

 the Archegosauria have been, I think it will be hazardous to take it 

 for granted that they had neither ventral scutes nor even persistent 

 branchial arches. 



If we adopt these two divisions and endeavour to range the known 

 Carboniferous Labyrinthodonts under one or the other, — Archego- 

 saurus, of course, takes its place among the Archegosauria; and Pho- 

 lidogaster*, I suspect, must go with it, though its vertebras are far 

 better ossified, and the condition of the cranial condyles is not known. 

 Baphetes and Parabatrachus are too little known to justify us in 

 arriving at any conclusion respecting them ; and the like is true of 

 Loxomma. As regards the Raniceps of Wyman (Am. Journ. of Sci. 

 and Arts, 1858), the Dendrerpeton and Hylonomus recently discovered 

 by Dr. Dawson in the Nova-Scotian coal-field, and the new genus 

 Eylerpeton instituted by Professor Owen, from the same locality, I 

 do not think we are even in a position to say that they are Labyrin- 

 thodont, much less whether they have Archegosaurian or Masto- 



* Whence the term ' Ganocephala ' as a distinctive appellation of the Arche- 

 gosauria is inadmissible. 



t It seems to me probable that the vertebral centra of Archegosaurus may really 

 have been osseous rings, such as are found in embryo frogs and salamanders, and 

 as persisted in Megalichthys and probably in Bhizochis, and that they have broken 

 into the separate pieces described by von Mever in the process of fossilization. 



t Quart. Journ. Geol. Soc. 1862' 



p'2 



