150 EEPTILIA. 



and the sutures between its component elements have not been clearly 

 distinguished. There is a double narial opening in front ; the orbits are 

 of moderate size, directed both laterally and superiorly; while the notch 

 or excavation of the postero-lateral border for the external auditory, 

 meatus is unusually large and deep, affecting even the quadrate bone. 

 The occipital condyle has not been seen. The mandible is not produced 

 behind its articular facette. Of the dentition, only the marginal series 

 have been observed ; these teeth being simple smooth cones, riot folded at 

 the base, in a single row in each jaw. Two of the anterior dorsal vertebrae 

 are proved to be amphicoelous, and large intervertebral wedge-bones occur 

 with them. The ribs are much expanded, but do not touch each other. 

 Upon them rests the carapace, consisting of a series of bilaterally sym- 

 metrical, transversely elongated bands of bone ; but the shield thus 

 formed does not appear to extend quite so far forwards as the occiput. 

 The bands of the carapace, which are at least twelve in number, alternate 

 with the supporting ribs, resting on their adjacent edges and separated by 

 narrow interspaces. In the anterior part the superior costal surfaces rise 

 between these bands to the plane of the latter, forming a closer surface 

 than posteriorly. The pectoral arch comprises a pair of bent clavicles, 

 expanded at each end, overlapping a short and broad interclavicle. The 

 coracoid is small, not notched, and may be co-ossified with the scapula. 

 The humerus exhibits a much expanded head and slender shaft. The femur 

 is longer than the tibia. Otoccelus occurs in the Permian of Texas, where it 

 seems to be represented by two species. The type form, 0. testudineus, is 

 known by an imperfect skull associated with remains of the pectoral arch 

 and fore limb, also almost certainly with two dorsal vertebrae, numerous 

 ribs, and part of both hind limbs. The type specimen of 0. mimeticus 

 exhibits the nearly complete skull and mandible in undoubted association 

 with the carapace and some limb-bones. The skull in each species 

 measures about 0'12 m. in length. 



Pariotichus and other genera, known by fine skulls and 

 other remains, also apparently represent the Pariasauria in 

 the ^ermian of Texas, U. S. A. 



Sub-Order 2. Theriodontia. 



Another group of Anomodonts is remarkable for the re- 

 semblance in form of the skull to that of the carnivorous mam- 

 mals, and in the differentiation of the marginal teeth (so far as 

 shape is concerned) into incisors, canines, and molars. The 

 sub-order they represent is thus named THERIODONTIA. The 

 external bones are never sculptured. There is a large supra- 

 temporal vacuity, the bones contracting into a single broad 



