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Show 9G DR. R. BROOM OX THE [Feb. 7, 6. On some Points in the Anatomy of the Theriodont Reptile Diademodon. By R. B room, M.D., C.M.Z.S., Victoria College, Stellenbosch. [Received December 29, 1904.] (Plate X *) Mr. Alfred Brown, of Aliwal North, to whom science already owes so much, has recently made another discovery of considerable importance. In the neighbourhood of Aliwal he has found a very well-preserved Theriodont mandible with a number of other well-preserved bones, all belonging to the same individual; and these he has kindly forwarded to me for examination and description. When the remains were fully developed it was found that we had two dentaries, two ilia, two ischia, a pubis, a femur, and a lumbar vertebra of Diademodon mastacus Seeley. Though the type specimen consists of only a fragment of maxilla with some molar teeth, the molars in the present mandible agree so closely in structure and size as to leave little doubt that the remains are those of D. mastacus. With the exception of the anterior part, both dentaries are well preserved, the hinder part of the left being in almost perfect condition. The symphysis is missing, but from the impression left it is pretty manifest that the two dentaries have been anchylosed in front. The dentary resembles that of Gompho-gnathus and Trirachodon in the very great development of its posterior portion. The coronoid process is of large size, but does not terminate in a posteriorly directed point as in most mammals. The posterior part of the dentary, as in Cynognathus, probably almost reached the articulation, and apparently overlapped the articular as in the better known Tlieriodonts. A small but distinct angle is formed, very similar to, but better developed than, that in Trirachodon. Behind the canine there is a short diastema of about 10 mm., and then a series of four teeth which may be regarded as premolars. Behind the premolars are seven molars. The first premolar is smaller than the others, but is imperfectly preserved. It probably, however, does not differ from the others in structure. Each of the posterior of three premolars is a rounded tooth in which the height is about twice as great as the antero-posterior measurement. When viewed from the outer side, each tooth appears to be a simple pointed cone, but in reality the top is about as broad as the base, owing to there being on the inside of the tooth a second cusp only a little shorter than the outer. The outer cusp in the unworn condition is probably finely Serrated on both its anterior and posterior edges. The fourth # For explanation of the Plate, see p. 102. |