88 DR. R. BROOM ON THE SKULLS OF BICYNODONTS. [Juiie 3, 



As the two specimens are* from the same locality and agree 

 closely in most of their characteristic features, it seems reasonable 

 to conclude that the differences in the maxillary development are 

 due to sex ; the male having the powei'f ul tusk directed downwards, 

 and the female the small tusk which is directed more forwards. 



The accompanying drawings (text-figs. 16 A & 16 B, p. 87) 

 delineate side views of the two specimens, partly restored. In 

 the male the lower jaw has been I'estored fi'om the jaw of 

 jD. leoniceps. 



That the differences are due to sex receives confirmation from 

 the skulls of other forms. 



The type of Owen's Dicynodon tigriceps is a skull with a very 

 powerful downwardly directed tusk. Near Pearston I have 

 discovered a skull which, though imperfect, agi-ees closely with 

 D. tigriceps in its posterior region, but the tusk is so inconspicuous 

 that at first one would think the skull belonged to a species of 

 Udenodon. As in the female 1). laiifrons, the tusk is directed as 

 much foi'wards as downwai-ds, and has a diameter of only half 

 that of the tusk of the male (Owen's type), though the skull is 

 even a little lai-ger in the female specimen. 



In Udenodo'ii-skulh we find similar differences in the maxillary 

 development — skulls with powerful downwardly-directed canini- 

 foi-m ridges, and skulls with feeble, flattened, foiwai'dly directed 

 maxillary processes. Owen'-s type of Udenodon baini is a good 

 example of what I believe to be a male skull. The little skull 

 which I have recently figuied as the type of U. gracilis^ is 

 probably a faii'ly typical female skull. I have in my possession a 

 skull which I believe to be that of U. baini, but which has a feeble 

 maxillary veiy much resembling that in the type of U. gracilis. 

 If it is not the female of U. baini, it must be of a new species ; and 

 as the differences in maxillaiy development are closely comparable 

 to those seen in the two types of I}ict/7iodo7i-iiku\h, one feels 

 justified in concluding that the specimens with the feeble maxillae 

 are females. 



Besides the differences in maxillary develoj)ment, it is probable 

 that when more perfect specimens are found a number of additional 

 correlated chaiucters will be discovered. The arches, so far as 

 preserved, are undoubtedly moi'e feeble in the female Dicynodon 

 latifrons, and it is probable that the squamosal will be found to 

 be less greatly developed than in the male. It is also highly 

 probable that the lower jaw in the female is less massive than in 

 the male. 



1 R. Broom, "On the Structure and Affiuities of Udenodon," Proc. Zool. Soc. 

 1901, vol. ii. p. 162. 



