THE OSTEOLOGY OF THE DIADECTIDAE 127 



In 1896 Cope described (Cope, 1896) from the Permian of Texas 

 two genera, which he called Otocoelus and Conodectes. These he 

 placed in a new family of the Cotylosauria, the Otocoelidae, which 

 he described as follows : 



Posterior border of the temporal roof excavated laterally by the meatus 

 auditus externus. Teeth present in a single row, not transversely expanded. 

 Ribs immediately overlaid by parallel transverse derm-ossifications which form a 

 carapace. 



In the presence of the meatus auditorius this family differs entirely from the 

 other members of the Cotylosauria. In the latter the vestibular space is inclosed 

 by the lateral part of the temporal roof, and has no distal inferior bounding wall. 

 The meatus results in the Otocoelidae, not merely from the excavation of the roof, 

 but also from the excavation of the posterior border of the suspense rium. In 

 Conodectes this excavation is not great, but in Otocoelus it is very considerable, 

 the proximal extremity of the suspensorium having the anterior position seen in 

 the Loricata and the Testudinata. It resembles the quadrate of the latter order 

 in the decurvature of the proximal extremity into a descending hook, which 

 partially bounds the meatus posteriorly. 



This meatal excavation constitutes an approximation in the Cotylosauria to 

 other and later orders of the Reptilia, where it is nearly universal. It is interesting 

 to observe that it precedes in time the division of the roof into longitudinal bars 

 by perforation, in the series of which the Otocoelidae form a part. This fact 

 renders it probable that it is from this family that the order of the Testudinata 

 has descended In this family the slight posterior concavity of the quad- 

 rate region of the Diadectidae is extended forward to a great distance, and the 

 osseous tympanum is produced farther outwards. 



Later, in 1898 (Cope, 1898), he erected this family into a dis- 

 tinct order, the Chelydosauria, defined as follows: 



These reptiles possessed a carapace of transverse osseous arches which extended 

 across the back from side to side in close contact. The anterior part of the 

 scapular arch below resembles the corresponding part of the plastron of a tortoise. 

 The temporal roof is excavated posteriorly for the auricular meatus. The order 

 is probably ancestral to the Testudinata and the Pseudosuchia. 



In his synopsis of the orders of the Reptilia he describes the 

 order as with the "scapular arch internal to the ribs; temporal 

 region with complex roof and no longitudinal bars. A presternum; 

 limbs ambulatory." 



Cope regarded the Otocoelidae as the only family of the new 

 order, but it will be seen from the following descriptions that the 

 Diadectidae must be included therein. The order Chelydosauria is 



