96 MR. OLDFIELD THOMAS ON [Feb. 6, 



other in the neighbourhood of El Khaur, a place about forty miles 

 north-east of Aden, and some twenty-five miles west of Shukra. 

 But, as might be expected, no definable difference is to be found 

 in the animals of the two localities. 



The notes on habits &c. placed in inverted commas have been 

 contributed by Mr. Percival. 



1. Papio arabicus, sp. n. 1 



a. $. Subaihi Country, about 60 miles north-west of Adeu. 

 Alt. 1000 metres, 16th October, 1899. 



" The mountains run up to nearly 2000 metres, but the Baboons 

 keep to the lower slopes." 



Allied, so far as can be determined from the female, to Papio 

 hamadryas, and therefore probably the form from Aden which 

 has been commonly referred — though without the examination of 

 specimens — to that species' 2 . But this is by no means certain, and 

 it may be that either the true P. hamadryas occurs naturally in 

 the Aden district, or that examples of it have been brought across 

 from Somaliland to Aden during the long-continued native inter- 

 course between the two places, and that the Aden herd is the 

 offspring of escaped specimens. 



But whatever may be the case with the herd occurring close to 

 the town of Aden, certain it is that the present specimen, which 

 was obtained by a native about sixty miles to the north-west, 

 cannot be referred to the true P. hamadryas. 



The main difference appears to be in size, but it unfortunately 

 happens that while the present example is a female, all the 

 available specimens of P. hamadryas are males, so that sexual 

 difference has to be allowed for in distinguishing the two forms. 



But greatly as the sexes of Baboons may differ in general size 

 and length of skull, the dimensions of the teeth, at least of the 

 cheek-teeth, seem almost or quite unaffected by sex. Thus of a 

 pair, male and female, of the East- African Baboon {Papio thoth) of 

 about the same age (the male slightly older, but both rather 

 immature), the following are the respective measurements (in 

 millim.) of the skull and teeth : — 



Combined lengths of 



Total length 5 upper cheek- 4 posterior lower Length of last 

 of skull. teeth. cheek-teeth 3 . lower molar. 



3 187 50 46 15 



$ .... 159 50 46-4 15-6 



The teeth are therefore of about the same dimensions in the 

 two sexes, in spite of the difference in the size of the animals 

 themselves. A similar result has been found in Man, and is, indeed, 



1 Preliminary notice, P. Z. S. 1899,"p. 929. 



- See Matschie, SB. Ges. nat. Freunde, 1893, p. 25. 



3 The anterior lower premolar in Baboons partakes of the sexual speciali- 

 zation of the canine, and has therefore to be eliminated in a comparison of this 

 sort. 



