1901.] Allen, Opossums of the Genus Didelphis. 163 



General Remarks. Northern specimens (New York and New 

 Jersey) are lighter in coloration and have softer and more abun- 

 dant and whiter underfur than those from the Middle States and 

 further southward; the blackish V-shaped area on the top of the 

 head becomes better defined and the incipient dusky spot in front 

 of the eye more pronounced in passing from northern localities 

 southward. As shown by the tables of measurements given be- 

 yond (see Table I), there is apparently very little geographical 

 variation in size; a large series of specimens might show a de- 

 crease in size toward the northern border of the range of the 

 species. The specimens at hand show a wide range of variation 

 in size, due apparently to age rather than to locality. 



The few specimens from west of the Mississippi River (Kansas, 

 Indian Territory, Oklahoma, and central and northern Texas) 

 do not differ appreciably from specimens from New York, Ohio, 

 Tennessee, Maryland, and North Carolina; but the material for 

 comparison is too scanty to warrant positive conclusions. 



Nomenclature. The nomenclature of this species, both generic 

 and specific, has of late been the subject of considerable discus- 

 sion. An attempt was recently made * to discard the generic 

 name Didelphis on the ground that the species, D. marsupialis 

 Linn. necessarily its type through the process of elimination 

 was indeterminable. By this ruling Didelphis Linn. (1758) was 

 replaced by Sarigua Muirhead (1819), and D. marsupialis Linn. 

 (1758) was disallowed as being unrecognizable. To both of these 

 rulings the present writer has taken exceptions. 3 Mr. Oldfield 

 Thomas 3 supports the retention of the name Didelphis, * but ex- 

 presses his preference for " retaining the familiar term virginiana 

 for the Virginia Opossum." 



As to the proper specific name, however, the case is more com- 

 plex. I have heretofore favored restricting the name Didelphis 

 marsupialis of Linnaeus to the Virginia Opossum, on the ground 

 that the only reference given by Linnaeus that is positively iden- 

 tifiable is his citation of Tyson, whose account is not only detailed 



1 Cf. Rehn, Am. Nat., Vol. XXXIV, July, 1000, pp. 575-578. 



2 Cf. Allen, this Bulletin, Vol. XIII, 1900, pp. 185-190. In this article the date of Muir- 

 head s genus Sarigua, as stated by Rehn, was claimed to be erroneous ; that it should have 

 been given as 1832 instead of 1819. As shown later, however, by Mr. Witmer Stone (Science, 

 N.S. XII, No. 305, p. 685, Nov. 2, 1900), the correct date is 1819, as given by Mr. Rehn. 



3 Am. Nat., Vol. XXXV, Feb. 1001, pp. 144, 145. 



4 Mr. Rehn also in a late paper (Am. Nat., XXXV, Feb. 1901, pp. 147-149) admits the 

 propriety of retaining Didelphis in place of Sarigua. 



