380 Geological Society : — 



character indicating, with the angular outline of the skull, the sub- 

 generic distinction. 



Ptychognathus verticalis. — The skull of this species, repeating the 

 subgeneric characteristics of the foregoing, has the facial contour 

 descending almost vertically from, and at almost a right angle with, 

 the fronto -parietal plane. Orbits proportionally larger and more 

 fully oval. Ridged sockets of the canine tusks descending more 

 vertically from below the orbits. Originals transmitted to the 

 British Museum by Governor Sir George Grey, K.C.B., from Rhen- 

 osterberg. South Africa. 



Subgenus Oudenodon, Bain (^ovdeis, none, bdovs, tooth). — The 

 skull in this subgenus presents the divided nostrils, the structure 

 and the rounded contours of that of the true Dicynodons ; also the 

 same form, relative size, and position of the orbits and nostrils ; 

 but the zygomatic arches are more slender, straight, and long ; and, 

 although there be an indication of an alveolar process of the supe- 

 rior maxillary, the lower part of which projects slightly beyond the 

 rest of the edentulous border of the jaw, it does not contain any 

 trace of a tooth, so that both jaws are edentulous, — a character which 

 had attracted the attention of their discoverer, Mr. Bain, who, in 

 indicating it, proposed the name Oudenodon. 



It is permissible to speculate on the possibility of these toothless 

 Dicynodontoids being, after the analogy of the Narwhals, the 

 females ; or of their being individuals which had lost their tusks 

 without power of replacing them, as the known structure of the 

 true Dicynodons indicates. But there are characters of the zygo- 

 matic arclies and temporal fossse which diiFerentiate the toothless 

 skulls sufficiently to justify their provisional reference to a distinct 

 subgenus. 



Hyoid apparatus of Oudenodon. — Beneath one of the skulls, 

 and imbedded in the matrix between the mandibular rami, were the 

 following elements of the hyoid apparatus : — basi-hyal, cerato-hyals, 

 thyro-hyals (or hypo-branchials), cerato-branchials, and uro-hyal. 



The cerato-hyals are long, subcompressed, expanded at both ends ; 

 the thyro-hj'als shorter and more slender ; the cerato-branchials 

 with a sigmoid flexure ; the uro-hyal symmetrical, broad, flat, semi- 

 circular, with a production like a stem from the middle of the straight 

 anterior margin. This apparatus shows the complexity by which 

 the hyoid in Lizards and Chelonians diflfers from the liyoid in Cro- 

 codiles, and combines Chelonian with Lacertian characters. Trans- 

 mitted by Mr. Bain from South Africa. 



Dicynodon tigriceps. — Pelvis : ilium, ischium, and pubis coalesced 

 to form an 'os innominatum,' with the sutm-e at the symphysis 

 obliterated. At least five sacral vertebrae ; the first with broad, 

 thick, triangular, terminally expanded pleurapophyses. The strong, 

 straight, trihedral ilium overlies the above sacral rib, and extends 

 forward to overlie also the last long and slender rib of the free 

 trunk (thoracic) vertebrie. There are no lumbar vertebrae. 



Pubis very thick, strong, with a broad anterior convexity resem- 

 bling that of the Monitor in its internal perforation and external 



