256 Bulletin American Museum of Natural History. [Vol. XVI, 



the tail becomes slightly longer, the white on the ears, tail 

 and toes is reduced, and on the latter is of irregular presence, 

 and there is a decided tendency to melanism. A very similar 

 dichromatic form occurs in southern Texas, with, however, 

 differently shaped nasals. In Mexico the same general type 

 prevails, but the head is much darker, the tail is generally, 

 but not always, much longer, the size varies with locality, as 

 also do other features. This same general style, with local 

 variations, ranges over Central and northern South America, 

 being everywhere dichromatic, and over eastern South 

 America to Uruguay, with, however, over this last area, a 

 tendency to a better- denned pattern of head markings. 

 Adopting the changes in nomenclature for the Mexican and 

 Paraguayan types proposed above, the members of the genus 

 Didelphis will stand as follows: 



List of the Species and Subspecies. 

 I. MARSUPIALIS GROUP. 



1. Didelphis virginiana Kerr. Eastern United States, ex- 



cept the Gulf coast. 



2. Didelphis virginiana pigra Bangs. Southeastern Geor- 



gia, Florida, and the Gulf coast region to Texas. 



3. Didelphis mes-americana Oken. 



Didelphis marsupialis ALLEN, Bull. Am. Mus. Nat. Hist. XIV, 1901, 



1 66. Not D. 'marsupialis Linn, restr. 



Mexico, from Puebla and Guerrero northward. Probably 

 should be separated into several local forms. 1 



4. Didelphis mes-americana teocensis Allen. Rio Grande 



region of Texas and Mexico. 



1 In this connection it may be of interest to note the results of an examination of 

 the types, so far as they are extant, of Bennett's Didelphis calif arnica and D. breviceps. 



A skull in the British Museum of one of the two specimens on which D. californica 

 Bennett was based (the skins are not extant) resembles, in the character of the nasals, 

 the Vera Cruz type of Mexican opossum, named by me D. m. tabascensis. As, how- 

 ever, Mr. Bennett's material, described as "from that part of California which adjoins 

 Mexico," of which this formed a part, appears to have been unquestionably Sonoran, 

 it seems better not to disturb the name already bestowed upon the east Mexican 

 form; especially in view of the inconstancy of the form of the nasals in all the forms. 

 The alleged type skull is labelled: " Taken from one of the Types of D. californica Ben- 

 nett, P. Z. S. 1833, p. 40. No. 11410. Brit. Mus. Reg. 55-12-26-190. Didelphys 

 marsupialis, L. Loc. California. Ex. Coll. Zool. Soc." 



The type of D. breviceps Bennett, still extant in the British Museum, is a rather 

 young specimen. On removal of the skull from the skin for examination it was found 

 to agree in the form of the nasals with Sinaloa specimens of corresponding age. 



