1896. J 1-^*^ [Cope. 



OTOCCELID.E. 



Posterior border of temporal roof excavated laterally by the meatus 

 auditorius externns. Teeth present in a single row, not transversely 

 expanded. Ribs immediately overlaid by parallel transverse dcrmoossi- 

 fications which form a carapace. 



In the presence of the meatus auditorius this family diifers from the 

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

 enclosed by the lateral part of the temporal roof, and has no distal inferior 

 bounding Avail. The meatus results in the Otoccelidse not merely from 

 the excavation of this roof but also from the excavation of the posterior 

 border of the suspensorium. 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 Tes- 

 tudinata. It resembles the quadrate of the latter order in the decurva- 

 ture of the proximal extremity into a descending hook, which partialh' 

 bounds the meatus posteriorly. 



This meatal excavation constitutes an approximation in the Cotylo- 

 sauria to other and later orders of Keptilia, 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 

 Otoco?lidie form a part. This fact renders it probable that it is from this 

 family that the order of the Testudinata has descended. It may also be 

 found that the Pseudosuchia have the same origin. The carapace of the 

 Otocoelidfe approaches nearly that of tlie genus Typothorax* Cope, of 

 the Trias ; where each rib is expanded, and bears above it a distinct 

 dermosseous band of equal width, with a sculptured surface. This 

 genus probably belongs to the Pseudosuchia, whose type genus Aetosau- 

 rus Fraas, lias a carapace consisting of transverse bands of osseous 

 plates in mutual contact. The transverse segmentation of the carapa- 

 cial bands of Otoccelns would produce such a structure. The same char- 

 acter is found in the genus Episcoposaurus Cope of the Trias, where the 

 cranium is unknown. A reduction of the number of the transverse 

 bands of the Otoccelidge would approximate the carapace to that of the 

 Testudinata. The arrangement of the clavicles and episternum is quite 

 like that of the corresponding elements in the anterior lobe of the plas- 

 tron in the tortoises. The median and posterior part of the abdominal 

 wall of the Otoccelidai is unknown. The teeth are quite insignificant, 



*Iu the last edition of Dana's Geology, 1895, p. 758, it is inaccurately stated that "A 

 large Crocodilian of the genus Belodon has been described by Cope .... under the 

 name of Typothorax coccinaruvi." The fact is, that two animals were included in the 

 description, which I afterwards determined to belong to different genera. The one for 

 which I reserved the name Typothorax does not belong to the genus Belodon. See Pi-oc. 

 Amer. Philos. Soc, 1887, p. 200. Plate I, where the genus and species are defined. Recently 

 Marsh has described {Amei: Jouni. Sci. Arts, July, 1896, p. 61) the cast of a similar rep- 

 tile from the Trias of Connecticut, to which he gives the name Stegomus arciiatiis. He 

 does not distinguish the supposed new genus Stegomus from Typothorax. 



PROC. AMER. PHILOS. SOC. XXXV. 151. P. PRIKTED AUGUST 12, 1806. 



