668 Bulletin American Museum of Natural History [Vol. LXVI 



and, in contrast to these changes, a loss of virtually all pigment in the 

 hair of the back, so that this area changes from one of deep bay, mod- 

 erately long hairs to one of short, dirty-white hairs. The hairs of the 

 distal two-thirds of the tail are uncolored throughout life, though the 

 underlying dermal pigment, particularly of the basal half of the tail, 

 may in the tanned skin, give a mottled pattern of yellow and gray. 



Sex differences in the skull are not found in this series, though from a 

 comparison with other material it seems probable that males attain 

 greater size than do the females. 



Age Differences. — Age changes in the skull are those of size, suture 

 obliteration, and proportion. The first sutures to be obliterated are 

 those separating the occipital elements, the parietal suture, and, later, 

 the suture between the interparietal and parietals. 



This later suture is open in a skull 250 mm. in greatest length, 

 whereas the others, which were open in one of 181 mm., are completely 

 obliterated in this larger skull. In skulls of yet older animals the parietal- 

 interparietal suture is closed. The occipitoparietal suture, however, is 

 open in the oldest specimens. Later the frontal suture closes progres- 

 sively from the rear. Fusion occurs along the nasal suture very sporadi- 

 cally, being found only in two young skulls. The most prominent modi- 

 fications of skull form are a great reduction in the proportionate degree 

 of inflation in the anterior frontal region, and marked increase in skull 

 length in proportion to skull depth. 



The teeth commonly regarded as the first and second molars, when 

 first erupted have two cones, but these are soon lost through wear. The 

 skull of a newborn individual on which these cones are displayed, also 

 shows double cones on the last premolar. On the left side two cones are 

 also present on the next to last premolar, while on the right the area is 

 occupied by two simple teeth which suggest a splitting of germinal 

 buds as the explanation of the large number of maxillary teeth reported 

 for the genus. The diameter of the teeth increases until maturity, but 

 with approaching senility the anterior teeth are lost, and the posterior 

 members may be slightly reduced in size. 



Races then, the characters of which are founded on color, size, 

 degree of frontal inflation, and tooth diameter must be critically ex- 

 amined with reference to the age class of the type. 



The skull measurements of the adult specimens are represented in 

 their averages, minima, and maxima in preceding table, pp. 666-667. 



Field Data. — Mr. Lang's field notes on specimens of this race 

 contain observations on anatomy, habits, and habitat, which may be 

 conveniently arranged according to subject matter. 



