80 Annals of the Carnegie Museum. 



teeth, the canines of the lower jaw being longer than the incisors, a 

 distinction deemed by some authors as perhaps hardly sufficient to 

 cause the Tamarins to become separated generically from their lela- 

 tives. Tamarins and Marmosets resemble each othei , and the 

 skulls with the large brain-case are much alike" (p. 179). 



Elliot gives a numbei of plates, each presenting foui views of skulls 

 of the several genera and species named above. The one of Seniocebus 

 (i3/^ natural size) is very good (Plate XXII). It closely resembles the 

 skull of Callithrix leucopus (Plate XXVII. 3^ larger than nat. size). 



There are but four or five skins of Seniocebus meticulosus in the hands 

 of science, and probably not more than three skeletons. One of the 

 latter appears to be in the American Museum of Natural History 

 (New York) ; I understand there is one in the U. S. National Museum 

 (not examined by me), and, finally, one prepared by myself, which 

 has been placed in the Carnegie Museum at Pittsburgh. Thus it 

 will be seen that this little monkey is one of the rarest species known. 

 The type was obtained in northern Colombia (Rio San Jorge). 



I have carefully compared in all of its details my skeleton of 

 Seniocebus meticulosus with the corresponding characters of the 

 skeleton, as presented in two adult skeletons and other osteological 

 material before me representing Callithrix jacchus, and I fail to find 

 any characters in the skeleton of the former (the teeth do not belong 

 to the skeleton) which point to such a thing as generic dift'erences 

 separating these two species. Some slight dilTerences aie apparent, 

 but they are entirely referable to individual variation, and it is 

 safe to say that they will not be found to be constant. The 

 fact that the canine teeth of the mandible in Seniocebus are longer 

 than the incisors, whereas they are not so in Callithrix, by no 

 means furnishes sufficient reason for creating a new genus for the 

 former. Moreover, although they are not quite as pointed as they 

 are in Seniocebus, we sometimes find the lower canine in Callithrix 

 jacchus somewhat longer than the outer incisor upon either side; so 

 that, too, proves to be a variable character among these species (Com- 

 pare Figs. 9 and 10 of Plate XVI of this paper) and consequently an 

 unreliable feature upon which to base generic differences. 



As is the case among human skulls, the facial angle differs in dif- 

 ferent individuals. For example, the facial angle in the skull of 

 Seniocebus I have in my collection is markedly less than it is in the 

 skull of that form figured by Elliot (Vol. i, Plate XXII), where it 



