4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 60 



Skull. — Smoothly rounded, flattened above, very broad across an- 

 terior roots of zygomata ; supraorbital and temporal ridges absent ; 

 postorbital processes faintly indicated in male only ; frontal region 

 broad, slightly constricted near point where postorbital processes 

 usually develop ; audital processes of alisphenoids and enclosed 

 bullae small ; incisive foramina reaching to posterior plane of canines. 



Measurements. — Type : Total length, 248 mm. ; tail vertebrae, 137 ; 

 hind foot, 19. An adult topotype : 240; 136; 17.5. Skull (average 

 of two adults) : Greatest length, 31. 1 (31-31. 2) ; condylobasal 

 length, 30.5 (30.2-30.8) ; zygomatic breadth, 16. 1 (16-16.3) ; nasals, 

 14. 1 x 3.4 (14.1 x 3.3-14.1 x 3.5) ; frontal constriction, 6.1 (6-6.2) ; 

 palatal length, 16.7 (16.5-17) ; upper molariform tooth row, 11 (10.8- 

 11.3) ; upper premolar series, 4.7+ (4.7-4.8). 



Remarks. — This pigmy opossum is very different from the other 

 Middle American species and I am unable to associate it with any of 

 those described from South America. It is characterized externally 

 by darker color than usual in the genus. The frontal constriction is 

 further back than in elegans which has similarly rounded supraorbital 

 borders. The type and topotype are at the molting stage. In the 

 type a patch of worn pelage remains on the anterior part of the 

 back, while in the topotype collected about a week later the molt 

 has progressed only as far as the head. 



Specimens examined. — Two, from the type locality. 



MICROSCIURUS ISTHMIUS VIVATUS, subsp. nov. 



Type from near Cana (altitude 3,500 feet), in the Pirri range of 

 mountains, eastern Panama. No. 179565, female adult, U. S. Na- 

 tional Museum (Biological Survey Collection), collected by E. A. 

 Goldman, June 5, 1912. Original number 21771. 



General characters. — Similar to istluuius, but upper parts paler; 

 under parts more orange buffy, less ferruginous. 



Color. — Upper parts, including outer sides of limbs, rather coarsely 

 grizzled black and pale orange buff or buffy yellow, the yellowish 

 element palest and clearest on head, and especially on cheeks ; under 

 parts orange buffy, clearest and strongest on under side of neck, 

 chest and inner sides of fore legs, becoming a lighter wash on belly 

 and inner sides of hind legs where the darker under color of the fur 

 shows through ; throat and ears buffy yellow, like cheeks ; feet 

 tawny ochraceous ; upper side of tail coarsely grizzled black and pale 

 buff, under side tawny ochraceous, with a black submarginal stripe 

 and grayish buffy edging, becoming pure black at tip. 



