CARBONIFEROUS LABYRINTHODONT 571 
permanently distinct epiotic bones, the divided supra-occipital, the 
three sculptured 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 /chthvosauria. 
But the drchegosauria have imperfectly ossified vertebral bodies, 
while the I/estedonsauria have them thoroughly well ossified, though 
still biconcave ; and the .J/as¢odonsauria have double ossified occipital 
condyles, which have not been found in Archegosaurta. 
Of the other distinctions, if such there were, of the two groups, we 
know very little. It is true that the drchegosaurta had, as von Meyer 
has proved, in his splendid monograph ‘ Die Reptilien des Stienkohls,’ 
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 A/astodonsauria ? 
Whatever may be the nature of the doubtful Axzsopus or Rhombopholts, 
it is certain that the African, probably Triassic, A/zcropholis was 
protected by ventral scutes; and until Mastodonsaurian Labyrin- 
thodonts are found preserved as favourably as the dArchegosauria 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 <Archegosaurta ; and 
Pholidogaster? 1 suspect, must go with it, though its vertebre 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 
HAylerpeton instituted by Professor Owen, from the same locality, I do 
not think we are even in a position to say that they are Labyrinthodont, 
much less whether they have Archegosaurian or Mastodonsaurian 
affinities. Among the many remains discovered by the zealous 
research of Dr. Dawson, I do not know that a single specimen of one 
1 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 A’hesodus, and that they have broken into the separate pieces 
described by von Meyer in the process of fossilization. 
2 Quart. Journ. Geol. Soc. 1862. 
