ipoi.] 



Allen, Opossums of the Genus Didelp.his. 



179 



Measurements of Skulls. 



Chichenitza, Yucatan. 



2 Merida, Yucatan. 



This species is based on three specimens from Chichenitza, 

 Yucatan (the type locality), four from Merida, Yucatan, two 

 from Apazote, Campeche, and one labeled simply " Campeche." 

 All are fully adult, with the crests of the skull highly developed 

 and the teeth more or less worn, except the Apazote specimens, 

 in which m A is in sight but not fully grown. Of these ten speci- 

 mens five are in the gray phase and five in the black phase of 

 coloration. The skins give the impression of a small, slender, 

 delicately formed animal, a feature well borne out by the skulls. 



Didelphis yucatanensis appears to be a very distinct form, 

 characterized especially by its small size, as compared with D. 

 tabascensis, found in the adjoining portions of Mexico and in 

 Guatemala, and D. richmondi of Nicaragua, by which it is geo- 

 graphically isolated from the small forms occurring in western 

 Colombia and Peru. It differs in the form of the nasals from 

 true D. marsupialis, which are pointed posteriorly instead of 

 being bluntly obtuse or more or less truncated on the posterior 

 border. In other words, they are of the usual or normal form 

 for the genus, as seen in D. virgimana, D. richmondi, and D. 

 tabascensis, etc. 



