Page:Synopsis of the Exinct Batrachia and Reptilia of North America. Part 1..pdf/30

 26 THE EXTINCT BATRACHIA, REPTILIA These 1 suspected to indicate the positions of inflections of enamel, as it is difficult to imagine such regularly radiating fractures. I cannot however, be entirely sure that this is the case. Under a low power neither the radii nor interspaees exhibit any structure ; the small pulp cavity is filled with the sandstone matrix hr which the tooth is enclosed. It may be supposed that the relatively denser structure of the enamel has been preserved in the slow alteration which the composition of the tooth has undergone. They thus project on weathered or ground surfaces. The species to -which these teeth pertain was originally described by the writer as a Mastodonsaurus. The latter genus however exhibits external grooves where the inflections of enamel enter and separate the dentine. These inflections, as is well known from the figures and descriptions of Professor Owen, are more or less convoluted, some of them very highly so. The lamina; of the teeth of the Eupelor cannot be looked upon as inflections of enamel, but rather as branches. They are exceedingly thin, and our sections do not demonstrate them to be double. If they are double, they are very much more attenuated than the external enamel stratum. They may be distinguished in a section of the wall of the pulp cavity at the base of the root as well as elsewhere. The fluted tooth referred to in my original description, in which this structure is observable, belongs apparently to a Thecodont, perhaps to Belodon : other teeth of this genus which I have seen present the same peculiarity. As the tooth from which the description of Eupelor was derived, is from the same stratum as the Belodon and Clepsysaurus, and some distance above the horizon of the eranial bones described, after an examination of the series in possession of Wheatley, I am disposed to refer all these teeth tOrthe Thecodonts, and restrict the name Eupelor durus rn. to the cranial bones only. Class II.-REPTILIA.. The following preliminary table exhibits the more essential characters of the orders of Reptilia, as understood by the riter :* I. Suprateniporal and postorbital bones present ; extremital portions of limbs not differentiated ; quadrate bone muted by sutures. ICHTHYOPTERYGIA. II. No supiatemporal or postorbital bones ; extremital portions of limbs differentiated. The quadrate bone united by suture to the prolific, the opisthotic and the quadra-tojugal bones. a The scapular arch continuous, including the sternum, which is anterior and simple. ARCHOSAURIA. • as Scapular arch not continuous, sternum inferior, extending posteriorly, composed of at least eight elements : dorsal vertebrce sacrum-like. TESTUDINATA. • A A The quadrate bone not united with the prolific, and articulating freely with the opisthotic ; no quadratojugal. (Streptostyhca.) Sacrum from three to five vertebrae ; anterior extremities excessively elongated for flight ; acetabulum complete ; pubes longitudinal, distinct ; exoccipital not distinct. PTEROSAURIA.
 * Many of these groups correspond with those proposed by Prof. Owen.