26 THE EXTINCT BATRACHIA, REPTILIA 



These 1 suspected to indicate the positions of inflections of enamel, as it is difficult to imagine sucli regularly 

 radiating fractures. I cannot however, be entirely sure that this is the case. Under a low power neither the 

 radii nor interspaces exhibit any structure ; the small pulp cavity is filled with the sandstone matrix in 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 cranial bones described, after an examination of the series in possession 

 of Wheatley, I am disposed to refer all these teeth to the Thecodonts, and restrict the name Eupelor durus m. 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 writer :* 



I. Supratemporal and postorbital bones present; extremital portions of limbs not 

 differentiated ; quadrate bone united by sutures. 



ICHTHYOPTERTGIA. 



II. No supratemporal or postorbital bones ; extremital portions of limbs differentiated. 

 A The quadrate bone united by suture to the prootic, the opisthotic and the quadra- 



tojugal bones. 



« The scapular arch continuous, including the sternum, which is anterior and simple. 



ARCHOSAURIA. 



aa Scapular arch not continuous, sternum inferior, extending posteriorly, composed of 

 at least eio-ht elements : dorsal vertebra? sacrum-like. 



O 



TESTUDINATA. 



A A The quadrate bone not united with the prootic, and articulating freely with the 

 opisthotic ; no quadratojugal. (Streptostylica.) 



Sacrum from three to five vertebras ; 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. 



