1901.] Allen, Opossums of the Genus Didelphis. 169 



Potosi, Durango, Guanajuato, and Queretaro, these States being 

 each represented by a single specimen. There are numerous 

 specimens from several points along the western coast, as 

 Acapulco, Manzanillo, Colima, Armeria, and Mazatlan. 



As shown later, a separable form occupies. the Lower Rio 

 Grande Valley, and another the coast region of Vera Cruz, 

 Tabasco, and Chiapas. 



Nomenclature. As already shown (p. 164), it seems best to 

 adopt, by the usual method of elimination for composite groups, 

 Linnaeus's name D. marsupialis for the large Mexican Opossums, 

 considering the name as tenable on the basis of the Tlacuatzin 

 of Hernandez, cited by Linnaeus. While no definite type local- 

 ity can be assigned, we may assume it to be that portion of 

 Mexico known to Europeans at the middle of the seventeenth 

 century, and hence assume as the type locality the region about 

 the city of Mexico. The name heretofore usually employed has 

 been Didelphis calif ornica Bennett, based on a specimen " from 

 that part of Mexico which adjoins California." The specimen 

 was collected by Douglass on his journey across Mexico, but no 

 definite localities have ever been given for the types of the various 

 species of mammals based on the collections made by him during 

 this trip. If they were taken in northwestern Mexico, as gener- 

 ally supposed, they must have been obtained from localities quite 

 remote from the present State of California. 



Mr. Bennett described in the same paper a Didelphis breviceps, 

 also based on a specimen collected by Douglass. The alleged 

 differences in respect to the proportions of the head with reference 

 to the position of the ear might easily be due to bad taxidermy. 

 In other respects the two alleged species agree very well for 

 animals of this group. D. pruinosa Wagner was described from 

 a specimen, from " Mexico," no definite locality being indicated. 



The specimens on which these supposed species were based 

 were all in the gray phase of pelage, and are characterized by the 

 great length of tail peculiar to the large Mexican Opossum. D. 

 breviceps and D. pruinosa must apparently be construed as pure 

 synonyms of D. calif or nica, which name is here referred to 

 D. marsupialis Linn, (restr.). 



The D. marsupialis group, as thus restricted, is separable into 

 several geographical races or subspecies, some of which can be 



