362 Microscopic Structure of the Teeth of the Lepidostet. 
Lepidosteus oxyurus, and that of the tooth of the Ichthyosaurus 
given by Prof. Owen in his Odontography, Pl. 64 B, fig. 3, it will 
be at once seen that in the former there is a much closer resem- 
blance to the Labyrinthodonts than in the latter; that is, in the 
Lepidosteus oxyurus the involutions of the cementum are much 
more extensive—although the Ichthyosaurus is described by Prof. 
O. as having teeth much more complicated in this respect than 
any existing animal. 
In comparing the teeth of the Lepidostei with those of the La-~ 
byrinthodonts, those of the former will be found much less com- 
plex than in a greater portion of the latter; though quite as much 
and even more so, than in the Labyrinthodon leptognathus, fig- 
ured in the Odontography, Pl. 63 B, fig. 1. Between the tooth 
of this last and that of the Lepidosteus oryurus, there is no ma- 
terial difference except in the size of the pulp cavity; the radia- 
tions of this last and the involutions of the cementum having 
precisely the same relative position in both. 
Thus we have the teeth of the Lepidostei, and some of the spe- 
cies of the Labyrinthodonts at least, reduced to the same type or 
plan of organization. In both the pulp cavity sends out its radi- 
ations, and in both the cementum is more or less prolonged in- 
wards, at regular intervals subdividing the tooth into numerous 
sections. ‘The calcigerous tubes in both cases are directed from 
the rays of the pulp cavity towards the investing cementum and 
its involutions. 
The question very naturally presents itself, whether some of 
the fossil teeth from the Warwick sandstone in England and the 
Keuper in Germany may not be referred to some extinct Sauroid 
fish, rather than the Labyrinthodonts, according to the views of 
Prof. Owen. ‘The former existence of gigantic Batrachian rep- 
tiles it is presumed will not be doubted, since it is based upon 
osteological evidence which it is impossible to controvert. But 
Prof. Owen informs us that in many instances the teeth from 
both the formations above mentioned, which were submitted to 
him for examination, were either mere fragments, or teeth de- 
tached from the jaws on which they grew. ‘These he very natu- 
rally referred to the Labyrinthodonts, no such peculiarities of 
structure having been shown to exist in the other Vertebrata, ex- 
cepting in a rudimentary form in the Ichthyosaurus, and the bases 
of the teeth of a few fishes. Since however the Lepidostei pre- 
