4 1 2 Bulletin American Museum of Natural History. [Vol. XIV, 



Skull. Type (young adult ? ) : Total length, 54 ; basal length, 51 ; length of 

 nasals, 27.5 ; width of nasals, 9 X 3-7 ; zygomatic breadth, 28 ; mastoid breadth, 

 16.5 ; interorbital breadth, 9.5 ; palatal length (from inner base of incisors), 

 30 ; breadth at m^, outside, 18 ; inside, n ; upper toothrow, 19.5 ; m 1 "*, n. 



No. 1-6-7-72, ad. $ with worn teeth : Total length, 55 ; basal length, 52 ; 

 length of nasals, 29 ; width of nasals, 9X4; zygomatic breadth, 28 ; mastoid 

 breadth, 17 ; interorbital breadth, 9.5 ; palatal length, 31 ; upper toothrow, 

 20 ; m 1 " 4 , 11.5. 



Young. Young examples, one-tenth to one-fourth grown, similar to adults 

 in general coloration, but in the very young with a strongly marked black dorsal 

 stripe, the cheeks and eye-spots brighter, approaching ochraceous buff. 



Metachirus bolivianos belongs to the M. nudicaudatus group, 

 but differs from all previously described members of it in the 

 blackish variegation of the back, black-tipped hairs being not 

 only a conspicuous feature of the dorsal coloration, but give in 

 some specimens the prevailing tone, especially to the median 

 area, which shows often a tendency to a distinct black median 

 band, which in the young appears as a distinct, sharply defined 

 line, wholly absent in young of corresponding age in M. nudicau- 

 datus (Guiana specimens) and in M. nudicaudatus colombica (from 

 near Bogota). It also differs from the other forms in the paler 

 coloration of the sides and abdomen, outside of thighs, and eye- 

 spots, with consequently greater contrast between the coloration 

 of the dorsal and ventral surfaces. The black of the dorsal 

 surface is about as in the M. opossum group, but with a pale yel- 

 lowish gray color instead of a clear gray. Apparently its nearest 

 ally is M. nudicaudatus phaur us Thomas from northern Ecuador 

 (type and only specimen, 1-3-19-44, $ ad., May 19, 1900, St. 

 Javier, N. Ecuador, alt. 60 feet ; G. Flernming). The type of the 

 latter is in short velvety pelage with a broad, ill-defined dusky 

 median area and a wholly "dark tail. This form corresponds to 

 the dark form tschudii of the M. opossum group from Peru. 



This subspecies is based on a series of n specimens, collected 

 by P. O. Simons at Chulumani, Bolivia, of which 5 are young of 

 various ages (2 nurslings, 2 apparently just old enough to shift 

 for themselves, and i about two-thirds grown) and 6 fully adult. 

 The series is very uniform in coloration, though varying a little 

 in the amount of black on the back, except that the two very 

 young specimens have the black median stripe more distinct than 

 the older examples. 





