14 DIDELPHYS. 
J. A. Allen. A Preliminary study of the South American Opos- 
sums of the genus Didelphis! Bull. Am. Mus. Nat. Hist., 1902, p. 249. 
Didelphis (sic) Linn., Syst. Nat., 1, 1758, p. 54. Type Didelphis! 
marsupialis Linneus. 
Size very variable; ears large; hind feet short; feet with five dis- 
tinct toes, all provided with nails except the first toe of the hind foot, 
which is large, opposed to the others in grasping, and is without a 
nail. Tail long, prehensile, partly naked; pouch complete; long, 
bristle-like hairs mingled with the fur; incisors small and pointed; 
canines large; premolars with compressed pointed crowns; molars 
with sharp cusps. 
KEY TO THE SPECIES AND SUBSPECIES, 
A. Size medium. PAGE 
a. “Tail black ‘only at. DAS ihsty cnuss opel D. yucatanensis 14 
b. Tail black for two-thirds its length....... D. y. cozumel@ 15 
B. Size large. 
a. Under fur white at base. 
a.’ Under parts grayish white. 
a.” Posterior end of nasals rounded....D. mesamericana 15 
b.” Posterior end of nasals acute ....... D. mm. texensts 06 
bio Under parts yellowish; vcs sane D.m. tabascensis 16 
b. Under fur orange buff at base.............. D. richmondi 16 
c. Under fur yellowish white at base. 
a.’ Head yellowish white to nape......... D. m, insulanis 17 
b.’ Head dark, spotted with white............ D.m, battyt 17 
c.’ Middle of head between eyes posteriorly, 
Diecleisht «0.6 chorale ache ads ete Pe es D. m. etensis 18 
13. yucatanensis (Didelphis!), Allen, Bull. Am. Mus. Nat. Hist., rgor, 
Dy tos 
YUCATAN OPOSSUM. 
Type locality. Chichen Itza, Yucatan, Mexico. 
Geogr. Distr. State of Campeche, and Yucatan, Mexico. 
Genl, Char. Similar in color to D. m. cauce (Allen, from southwest- 
ern Columbia) but smaller. Black and gray phase equally represented. 
Color. Male, upper parts black, base of hairs white; beneath 
grayish white; limbs, hands, and feet black; tail black at base; 
remainder flesh color; ears black. Female similar to the male, but 
covered with long yellowish white hairs, causing her to appear much 
lighter, and the black at base of tail is more extensive; under parts 
yellowish. 
Measurements. Total length, 634-756; tail, 312-393; tarsus, 
54-60. Skull: total length, roo; basal length, 90; zygomatic width, 
