108 Proceedings of the Biological Society of Washington. 



Similar to those of D. m. etensis of the adjacent mainland, and D. m. 

 colombica, but zygomata narrower anteriorly, more abruptly turned out- 

 ward posteriorly, the aides less nearly parallel ; premaxillse broader, but 

 less extended posteriorly, the outer borders notched or indented near 

 posterior tips; nasopremaxillary suture longer owing to shortening of 

 premaxillse ; frontopremaxillary line of contact between nasal and lachry- 

 mals longer; rostrum similar to that of D. m. columbica, broader than 

 that of D. m. etensis ; molars slightly smaller than in mainland forms. 



Measurements. — Type : Total length, 820; tail vertebrae, 405; hind foot, 

 64. An adult female topotype: 800; 410; 60. Skull (type): Greatest 

 length, 102.5; zygomatic breadth, 58.2; breadth of rostrum in front of 

 antorbital foramina, 20.3; postorbital constriction, 10.1; length of long- 

 est nasal, 49; length of nasopremaxillary suture, 10; length of nasomax- 

 illary suture, 22.8; maxillary toothrow ( back of last molar to front of 

 canine), 44.5. 



Remarks. — Like the other mammals of San Miguel Island this opossum 

 is clearly allied to forms inhabiting the adjacent mainland. In contrast 

 with the subspecies occupying Coiba Island the face is light in color. The 

 differential cranial characters noted are rather slight, but apparently dis- 

 tinctive. The type and topotype are in the black phase. 



Specimens examined. — Two, from the type locality. 



Marmosa mexicana savannarum, subsp. nov. 



SAVANNA MARMOSA. 



Type from Boqueron, Chiriqui, Panama. No. 18,915, c? subadult 

 (molars slightly worn), American Museum of Natural History, collected 

 by J. H. Batty, October 31, 1901. Original number 883. 



General characters . — Allied to Marmosa mexicana isthmica and Marmosa 

 mexicana zeledoni, but much smaller and paler than either; upperparts 

 more ochraceous ; fur on middle of throat and chest nearly pure white to 

 roots, instead of light buffy as in M. m. isthmica. 



Color. — Type: Upperparts between ochraceous — tawny and cinnamon- 

 brown (Ridgway, 1912), darkest on top of head and over back, becoming 

 more tawny on shoulders and outer sides of fore limbs, and lighter 

 ochraceous-tawny on flanks and outer sides of hind limbs; chin, middle 

 of throat, chest, and median line of abdomen nearly pure white to roots, 

 rest of underparts near light ochraceous- buff; orbital areas black as 

 usual in the group; feet (epidermis) yellowish, the hind feet clothed above 

 with short whitish hairs ; tail brownish, slightly darker above than below. 



Skull. — Much smaller and more slender, but in general structure essen- 

 tially like that of M. m. isthmica. 



Measurements.— Type: Total length, 267; tail vertebrae, 147; hind foot, 

 20. Skull (type): Greatest length, 32; condylobasal length, 30.8; width 

 of braincase over audital bullae, 11.4; zygomatic breadth, 16.7; nasals, 

 19.5x3.9; interorbital breadth, 5; palatal length, 17.8; upper molari. 

 form toothrow, 12.1. 



Remarks. — Contrasted with its geographic neighbors this small opossum 

 is sufficiently distinguished by small size and pale coloration. The latter 



