1859.] OWEN REPTILIAN FOSSILS. 49 



April 20, 1859. 



Kobcrt Folkestone Williams, Esq., 76 Coleshill Street, Eaton 

 Square, and Phillip Debell Tucker, Esq., 36 Holford Square, were 

 elected Fellows. 



The following communications were read : — 



1. On some Reptilian Fossils from South Africa. By Professor 

 Owen, F.B.S., F.G.S., &c. 



(Plates I. II. III.) 



Genus Dicynodon: Subgenus Ptyceognathus*, Ow. 



This subgenus is founded on four skulls, forming part of the collec- 

 tion transmitted to the British Museum in 1858, by His Excellency 

 Governor Sir George Grey, K.C.B., from tho sandstone rocks at the 

 foot of the Bhcnosterberg, S. Africa. These skulls belong, by their 

 dentition, to the Dicynodont family, but present such strongly 

 marked deviations from the type species of the genus {Dicynodon 

 lacerticq>s, Ow.) as to indicate a distinct subgeneric section; they 

 were accordingly entered in the Museum list, and labelled in the 

 cabinet where they arc exposed to view, under the term Ptychognatlius. 



Dicynodon {Ptychognatlius) dcclivis, Ow. (Plate I. figs. 3, 4, 5.) 



In this species, assuming the horizontality of the upper (fronto- 

 parietal) plane of the cranium (PI. I. fig. 3 n) as giving the natural 

 position of the skull, the broad plane of the occiput meets the fronto- 

 parietal plane at an acute angle, rising from the condyle upwards and 

 backwards — a direction not hitherto observed in any reptile, and 

 similar to that presented by the occiput in relation to the vertex in 

 the feline and many other gyrencephalons mammals. 



The fronto-parietal plane (ib. fig. 5) is bounded by an anterior 

 ridge, n, 15, extending from one superorbita] process to the other, 

 with a gentle convexity forward, including the interorbital space. 

 Prom this ridge the facial part of the skull ( tiir- 3 15. ■*•*) descends 

 in a straighl line in a direction nearly parallel with that of the 

 occiput, but slightly diverging from that parallel as it extends down- 

 ward and forward. The occipital ridge 1 fig. tr, s) is much produced, 

 and i.s deeply notched at the middle, the sides of the notch being 

 continued forward and gradually subsiding on the parietal plane as 

 they curve outward to die postfrontals (fig. 5). In the middle of 

 the fronto-parietal surface is a transverse pair of tubercles. The 

 occipital plane, owing to the outward expansion of the masto-tym- 

 panie plate-, (fig. I ^. «s), becomes the broadest part of the skull. 

 which quickly contracts forward to the ridged beginnings of the 



alveoli Of the canine tusks (fig. .'. -..|). 



* Prom rrTrl (gen -- old, nml yv & f fo s, »j»w. 



VOL. \\ I. r WIT I. ■ 



