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Show 1904.] TRIASSIC REPTILE TELERPETON ELGINENSE. 479 It is extremely regrettable that our knowledge of the American Cotylosauria should still be so meagre, but what we know shows them to be a type closely related to the Pariosaurians, though differing from them in at least one important character, the absence of the cleithrum. The same may be said of the Proco-lophonia (Procolophon and Telerpeton), and therefore these must be regarded, in the light of our present knowledge, as pertaining to the same group, for which the earlier name Cotylosauria should be used. The order Cotylosauria may be defined as thecodont Reptiles with the temporal region roofed over (without or with a single temporal foramen), with clavicles and interclavicle, with coracoids and prsecoracoids (epicoracoids), without or with a very vestigial plastron, and with the number of phalanges as in typical Reptiles. The absence of cleithra and the presence of more than 2.3.3.4.3 phalanges * distinguishes them from the Pariosauria ; the second character and the roofing over of the postorbital part of the skull distinguish them from the Anomodontia; whilst the presence of ossified prsecoracoids and the absence or extreme reduction of the plastron separate them from all the other primitive orders, such as Rhynchocephalia, Plesiosauria, Theco-dontia, &c, with the possible exception of the Pelycosauria, which likewise flourished in Pernio -Triassic times. The order Cotylosauria would comprise four families, the definition of the American types being derived from the contributions of Cope t and of Case +. A. Supratemporal roof broad, orbit small, nearly in the middle of the length of the head; no latero-temporal vacuities ; upper surface of skull more or less sculptured. Teeth small, not transversely expanded, in two rows in the posterior part of the jaws 1. Pariotichidre. Lateral teeth large, with the crowns expanded transversely to the axis of the jaw, in a single series 2. Diadectida. B. Supratemporal roof narrow, orbit very large; skull smooth; lateral teetli expanded transversely to the axis of the jaws. No latero-temporal vacuity 3. Telerpetida. A small latero-temporal vacuity 4. Procolophonida. In his important memoir quoted above, Prof. Osborn has proposed a diphyletic arrangement of the Reptilia with which I would be disposed to agree but for the inclusion of the Chelonia and Plesiosauria in the Synapsida, which comprise the Pariosauria, Cotylosauria (exclusive of the Procolophonia), and Anomodontia, and of the Procolophonia in the other subclass, named Diapsida. Both subclasses were evidently derived from Stegocephala w ith the temporal region completely roofed over. The Pariosauria were probably connected with the Labyrinthodontia and led to * I cannot understand what can have induced Dr. Broom to restore Pariosaurus with 2.3.4.5.4 phalanges in the manus and in the pes. The formula is 2.3,3.4.3 in the specimen in the British Museum. f Proc. Amer. Philos. Soc. xxxiv. 1895. p. 436. X Zool. Bull. ii. 1899. p. 231. |