1904.] PECULIARITIES IN CERTAIN MAMMALS. 419 



Thei'e ai^e, of course, cases where we are at a loss to give the 

 proper explanation of a numerical variation — to state, that is, 

 which of the teeth is the supernumerary ; but that depends often 

 on particular circumstances inherent to the species, as in the case of 

 an Ateles marginatus in the Natural History Museum (No. 1214 b), 

 on which great stress has been laid. This specimen has four 

 premolars in each upper jaw instead of three. "There is nothing 

 in this specimen to indicate that any of these teeth should be 

 considered supernumerary more than any other ; and in the 

 absence of such evidence it would, as I think, be best to regard 

 the four premolars in this specimen as collectively representing 

 the three premolars of the normal. For just as a stick may be 

 broken into three pieces or into four, so would it seem to be with 

 Multiple Parts."* 



The simile Avould be appropriate if Ateles marginatus, or the 

 other species of the genus, presented us with numerous instances 

 of foui- premolars ; but among hundreds of examined specimens 

 this is the only one in which the ■' stick " has been broken into 

 four " pieces." The reason why we cannot in this instance state 

 which of the four teeth is the supernumerary, depends on the 

 exceeding likeness in size and shape between the upper premolars 

 of Ateles. If instead of being acquainted with only one stage in 

 the life-history of this specimen, we had been able to watch it 

 from its childhood and follow the gradual development and 

 coming in place of the joremolars, we would presumably not 

 have been left in the dark as to the individualities of the premolars 

 in question. 



II. Two foetal skulls of the Springhoh (Antidorcas euchore Zimin.), 

 one undoubtedly female (text-fig. 80, p. 420), the other probahly 

 iniale (text- fig. 81) ; both exhibiting calcified upper canines. 



The diy skulls were kindly forwarded to me by our corresponding 

 member, Dr. R. Broom, of Pearston, South Africa, who previously 

 wrote to me that he had found small canines in male (?) and 

 female Springboks before birth, adding that he thought they never 

 cut the gum. 



The female skull, which appears to be slightly younger than 

 the other, has a basal length of 47 millim. ; the second deciduous 

 molar is about to cut the gum, the first and third being slightly 

 more retarded. The antero-inferior tapering termination of the 

 maxillary presents on either side a shallow furrow, in which is 

 imbedded a diminutive somewhat club-shaped tooth, in a pro- 

 cumbent position, parallel to the long axis of the skull. The 

 anterior portion of the tooth, which is scarcely over 1 millim. 

 long, is thicker than the posteiior ; the latter shows an oj)en root, so 

 that the tooth may not have attained its full length. In the second 

 skull, which, according to what Dr. Broom informs me, is pre- 

 sumably that of a male, the shape of the teeth is the same as in the 



* Bateson, op. cit. up. 113, 114. 



Proc. Zool. Soc— 1904, Vol. I." No. XXVIII. 28 



