1936] Halt, Hyraxes Collected by American Museum Congo Expedition 123 



both Procavia j. lopesi and Dendrohyrax d. emini where the sex of any 

 adult may be easily recognized by these teeth. 



The size of the skull in the Congo species seems to be uncorrelated 

 with sex as was also recognized by Thomas for the hyraxes as a whole. 



Sex differences in the skulls of the Procavia j. lopesi and Dendrohyrax 

 d. emini are not the same. In the latter, one observed difference is that 

 the skulls of the males are more massive and rugged, the ridges overlying 

 the roots of the incisors larger in the males, reflecting the larger size of the 

 teeth. 



Sex differences in the skulls of the rock hyraxes of Aba (Procavia j. 

 lopesi) are centered about the muzzle and the incisors, reflecting a better 

 fighting equipment in the males. Thus the heavy bony ring at the gum 

 line of the incisors is in the males enlarged and rough, and the muzzle is 

 slightly more massive. Most striking is the difference in the maxillary 

 root of the zygomatic arch, the outer surface of which in all adult males 

 is deeply concave, while in the females and young (Stage V) males it 

 slopes gently from the gum line to the maxilla-malar suture. For pur- 

 poses of sex diagnosis this is second in usefulness only to the shape of 

 the incisors. The mandibular symphysis further reflects the increased 

 strength of the male buccal region in the development of sharply de- 

 lineated ridges which carry forward the line of the lower mandibular 

 borders and pass upward to meet high on the symphysis. 



In the males of this species there is the further difference that the 

 frontal bone is on the average flatter and broader than in the females. 



The Ages at Which the Upper Canine Is Lost 



The deciduous canine is lost at different ages in different genera, as 

 Hahn has shown. My own figures, given below, bear out his conclusion 

 that in Procavia the tooth is lost before Stage V; that in Heterohyrax 

 it may be retained in Stage V; and in Dendrohyrax dorsalis is always 

 present to at least Stage IV and commonly to Stage VII. 



In Procavia j. lopesi the five specimens in Stage III all retain the 

 upper tooth which Lataste (1886, Ann. Genova Mus., (2) IV), con- 

 cluded was a canine, whereas all specimens in stages older than this have 

 lost this tooth. The Matadi hyrax (H. chapini) does not have this 

 tooth in the specimen in Stage VIII, but does in the other which is in 

 Stage V. The canine is retained in all specimens of D. d. emini, seven in 

 number, of Stages I to V and is lost in the six specimens of Stages VI 

 and VII. There are twenty-four specimens in Stage VIII, in twenty- 



