214 
Annals of the Tkansvaal Museum. 
identify certain portions of the coalesced bone with the composing 
parts. It seems to me, for example, that the downward process of the 
coalesced bone is part of the prearticular, and this for the following 
two reasons : The ridges of the separate part of tlie prearticular 
increase in height backwards, and it is therefore very probable that the 
bone forming the intricate suture behind also belongs to the pre- 
articular. The high margin of the articulation surface behind gives 
the impression that this is the end of the articular. I therefore 
presume the original boundaries of the bones to have been as indicated 
in figs. 5, 6, and 7. 
The Opercular . — The opercular elements are situated in the distal 
part of the jaw. They are coalesced in the symphysis (figs. 2, 10, 17). 
Directly behind the symphysis they occupy about two-thirds of the 
height of the jaw (fig. 14), but they gradually diminish in height 
towards the back till near the inner opening of the vacuity in the jaw. 
Here the end is divided into two unequal parts by a longitudinal 
notch. The upper part covers a small portion of the inner surface of 
the prearticular, and then breaks off abruptly. The lower part, which 
ends in a point, is situated below and a little to the outside of the pre- 
articular. The opercular is thinnest behind, and becomes gradually 
thicker forwards, the angular at the same time thinning out. There 
is a groove in the upper border of the opercular towards the symphysis, 
accommodating the lower border of the inner wall of the dentary (figs. 
14, 16). The narrow pit on the border of the opercularia and the 
dentaries in the symphysis continues forwards through two-thirds of 
the symphysis, and then bends sharply upwards, parallel with the 
front surface of the symphysis (fig. 1). A triangular surface of the 
coalesced opercularia is visible in front at the lower end of the sym- 
physis (fig. 3). 
The Complement arm — There is no separate bone which can be 
taken to be the complementary. It appears to me, however, that the 
bone has coalesced with the hinder end of. the inner wall of the 
dentary (fig. 2). There is a separation in this region in one specimen 
between a thin plate which clearly belongs to the dentary and a broad 
inner part which bears the continuation of the groove on the dentary 
(fig. 9). It could not be made out whether this separation is a suture 
or a fracture. The other ramus does not show this separation. Ad 
examination of many other specimens on this point gave no result. 
This investigation, however, rose the presumption that the comple- 
mentary could very well have coalesced with the inner wall of the 
dentary, the hinder part of which forms a very obtuse angle with the 
fore part. Definite proof of the presence of a complementary has, 
however, not been obtained. 
Dimensions . — The following dimensions were taken from Pal. 
Cat. No. 3099 (figured in figs. 1-4, and 9) : — 
Lengdh of the left ramus 105 mm. 
Height of the symphysis . 45 mm. 
Height of tlie left ramus over the centre of the 
outer opening of the vacuity 36 mm. 
Length of the left dentary 73 mm. 
Length of the left outer opening of the vacuity ... 34 mm. 
Length of the left inner opening of the vacuity ... 41 mm. 
Length of the visible outer portion of the angular 60 mm. 
Length of the visible surface of the opercularia on 
the outer surface of the symphysis 14 mm. 
