358 
simple, conical form, with numerous fine longitudinal striations ; 
and the teeth transmitted to Mr. Owen from the Warwick sandstone 
by Dr. Lloyd, beara very close‘resemblance to them. Their external 
characters not being sufficient to establish either specific or generic 
identity, Mr. Owen had sections prepared for microscopic examina- 
tion of portions of teeth of the Labyrinthodon Jaegeri forwarded to 
him by Prof.’ Jager, and of the English reptile; and though, from 
his previous examination of the intimate texture of the teeth of the 
Plesiosaur, Megalosaur, as well as of the Crocodile, Monitor, and 
most recent Lacertians, he did not hope to detect such modifications 
of structure as would obviously mark specific or even generic iden- 
tity, yet the slices exhibited such decided characters, and those of 
the/German fossils agreed so intimately with the sections obtained 
from the Warwick specimen; that Mr. Owen was enabled not merely 
to separate these fossils from all known reptilian animals, but to 
establish ‘a generic community of character in the-Keuper and sand- 
stone remains. ‘It was not, however, until, he had caused sections 
to be made in various directions, and. had studied them attentively in 
comparison with the teeth of true Saurians, Batrachians, and .6ther ~ 
animals; that -he'was enabled to comprehend the principle of the 
singular, cerebriform convolutions which pervade the dental struc- 
ture. of this remarkable reptile. ..The base of the tooth of the [ch- 
thyosaurus approaches: most nearly in character to the peculiarities 
of nearly the entire tooth of the Labyrinthodon. It.is impossible to 
convey clearly without illustrations the structure alluded to. It 
may, however, be stated, that in the fang of the tooth of the Ichthy- 
osaurus vertical folds of the external layer of cement (the enamel 
eeasing at the-base of the crown) are inflected inwards, at pretty 
regular.distances around the. circumference of, the tooth, towards 
the centre te a distance about equal the breadth of. the interspaces 
of the inflected: folds ;, the interspaces being occupied by correspond- 
ing processes ‘of the dentine, which radiate from the central mass 
of that-snbstance. . The thickness of this, interblended cement and 
dentine, surrounding the pulp-cavity, is about one-eighth of the dia- 
meter.of the-tooth. ».. | Bion vaderra 
.«Dhe plan.and:principle of the structure of the tooth of the Laby- 
ninthodon are the,)same as those of the tooth of the Ichthyosaurus, 
but they are carried out to the highest degree of complication... The 
converging vertical folds of the external cement are continued close 
to the centre of the tooth, and, instead of being straight, simple la- 
melle, they present a series of irregular folds, imereasing m com- 
plexity as, they proceed inwards, and:resembling the labyrinthie an- 
fractuosities of the surface of the braim; each converging fold is 
slightly dilated at its termination close to. the pulp-cavity.. The 
ordinary laws of dental structure-are, however, strictly adhered. to; 
and every space intercepted by a.convolution of the folds of the 
cement. is occupied by corresponding processes of the dentine. 
These charaeters-~were presented by a transverse section of a. frag- 
ment of a tooth of the Labyrinthodon Jaegeri from the German 
Keuper, which included about the middle third part of a tooth, 
