436 Professor H. G. Sceley—New Cape Labyrinthodont. 
grooved vomerine tooth of Labyrinthodon; it curves slightly inward 
(Pl. XIX, Fig. 2). On the inner side of the teeth the dentary bone 
rises in the same smooth rounded surface as in the other fossil, but 
externally an osseous cement appears to extend on to the tooth from 
the alveolar border. 
The second inner row of teeth originates just behind the anterior 
fracture, and includes indications of about twelve close-set teeth, 
carried in a groove which gradually widens as it extends backward. 
The teeth are smaller than the dentary series, but the crowns resemble 
them in all ways, being similarly compressed from front to back and 
wedge-shaped. The early crowns are broken, and several are missing 
from their sockets. These teeth are implanted in the bone which 
extends down the jaw between the dentary bone and the splenial, 
which is probably the surangular bone. Below the suture the splenial 
bone is rounded and shows no trace of the angular condition of the 
other specimen. ‘The base of the jaw is less flattened, traversed by 
three rather stronger little ridges; but the two sutures which are so 
marked a feature of the specimen from Aliwal North are not visible. 
The external lateral groove on the dentary bone becomes a circular 
tubular canal as it extends backward, running below the teeth. This 
groove is characteristic of Ichthyosaurs. A fine suture appears to run 
down its length, as in the fragment from Aliwal North separating the 
lower half of the bone as infra-dentary. The presence of such an 
ossification is an interesting approximation to the condition in 
Holoptychian fishes, in which Dr. Traquair’s specimens show two 
parallel rows of teeth; and those fishes have their tooth substance 
folded in a way that approximates to Labyrinthodonts, and especially 
to this fossil. 
The presence of these five bones in the mandible, which does not 
include the articular bone or the coronoid in the specimens preserved, 
appears to show that some South African Labyrinthodonts include 
seven bones in each ramus of the mandible. This character may not 
vary the general reptilian affinities of the skull, but appears to be 
a departure from the reptilian type in the mandible, which may 
approximate towards a lower type. The additional bone in the 
mandible is quite distinct from that described by Dr. Branson. 
EXPLANATION OF PLATE XIX. 
Fig. 1.—Transverse anterior fracture of ramus of mandible in Aliwal North 
specimen, showing bones about the Meckel cartilage cavity (M.); 
dentary and infra- ‘dentary externally, surangular and angular internally, 
overlapped by the splenial bone on the inner side. a, anterior end. 
2.—Transverse section, much enlarged, of part of a dentary tooth of the 
same specimen. The section was prepared by Professor Chapman, of 
Melbourne, and photographed by A. Campion, Hsq., in the metallurgical 
laboratory, Coopers Hill. 
», 3.—End view of the Middelburg specimen in the Munich University Museum, 
showing an entire external tooth, with natural curvature of the crown. 
,, 4.—The same specimen seen from above, showing a succession of empty tooth 
sockets on the mandible. 
Figs. 1, 3, and 4 are of the natural size. 
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