ON A FOSSIL REPTILE. aw 
41. Procolophon trigoniceps, a Cotylosaurian Reptile from 
South Afriea. By D. M. 8. Watson, M.Sc., F.Z.S., 
Lecturer in Vertebrate Paleontology in University 
College, London. 
[Received May 18, 1914: Read June 9, 1914. | 
(Plates I.-ITi.* and Text-figures 1-5.) 
INDEX. 
Page 
Structureweyei 7 ae ee eect | Yio 
Systema ticpae yen cca eee erence) 6 HA: 
The little reptile Procolophon has long been known, and the 
work of Owen, Seeley, Woodward, and Broom has made us 
acquainted with much of its structure. During my visit to South 
Africa, I was fortunate enough to collect in the original locality, 
Donnybrook, Upper Zwaart Kei, Dist. Queenstown, a nearly 
complete skeleton (hereafter referred to as the female skeleton) 
and several skulls and fragments. On the farm, Haslop Hill, 
which lies about fifteen miles north of Donnybrook, I obtained 
another almost absolutely complete and very well - preserved 
skeleton, which I shall call the male skeleton. 
This material, together with that in the British Museum, is 
perhaps the most extensive in existence for the study of any 
early reptile, and gives knowledge of almost every detail of the 
structure. 
Skull.—The general structure of the skull has long been known, 
but it is now possible to deseribe the basis cranii and brain-case 
in detail. 
The basioccipital is a comparatively small bone whose posterior 
end is formed by the transversely widened condyle, which is 
rounded. The upper surface of the bone carries the exoccipitals 
at the sides,-and the middle part of its upper surface is somewhat 
depressed and supports the brain. On the ventral surface the 
bone is soon covered by the basisphenoid but contributes to 
the tubera. 
The basisphenoid is a large and remarkable bone; on its lower 
surface two strong ridges continue the tubera forward and termi- 
nate in the basipterygoid processes, whose flat articular faces look 
well to the front. It is possible that the basipterygoid process 
is pierced by a foramen Vidii, but this is not certain. Between 
these ridges is a very deep groove, which in front passes upwards 
into the skull, separating the basipterygoids. From the sides of 
the bone immediately below and in front of the fenestra ovalis, a 
short but relatively powerful process passes outwards and back- 
wards and ends freely. On the upper surface the basisphenoid is 
a 
* For explanation of the Plates see p. 747. 
