210 Proceedings of the Biological Society of Washington. 



condylobasal length, 51.5; zygomatic width, 25.6; braincase, 21; maxil- 

 lary toothrow, 10. Tail is always long, 350 mm. or over. 



Remarks. — This subspecies is rather intermediate so far as its color is 

 concerned between the typical form and Rattus fremens. In the posses- 

 sion of its long tail it is clearly related to vociferans vociferans. 



Specimens examined. — Nine from Tapanuli Bay and one from Tarussan 

 Bay. 



Rattus virtus new species. 



1903. Mus firmus Miller, Proc. U. S. Nat. Mus. , vol. 26, p. 461, February 

 3, 1903. Not Mus firmus from Linga Island. 



1908. Mus firmus Lyon, Proc. U. S. Nat. Mus., vol. 34, p. 645, Septem- 

 ber 14, 1908. Not Mus firmus Miller from Linga Island. 



Type specimen. — No. 144223, U. S. Nat. Mus., skin and skull of adult 

 male, collected in eastern Sumatra, along Siak River, near mouth of 

 Gasip River, December 10, 1906, by Dr. W. L. Abbott; original num- 

 ber 4944. 



Geographic distribution. — Sumatra. 



Diagnostic characters. — A member of the Rattus firmus group of rats 

 distinguished from R. firmus chiefly by its more slender skull, especially 

 pronounced in the rostral and interorbital regions. 



Color. — The color of Rattus virtus is indistinguishable from that of its 

 allies, R. firmus* and R. validus.\ Upperparts and sides of head, neck 

 and body, and outerside of legs a coarsely grizzled mixture of blackish 

 brown and honey yellow (or color approximately that), the darker color 

 somewhat in excess on the upper parts, and both colors about equally 

 mixed on sides and legs ; entire underparts including inner side of legs, 

 ivory yellow, from base to apex of hairs. 



Pelage, etc. — Without spines, but along the upperparts, especially lower 

 back, rather thickly interspersed with rather long bristly hairs; tail with 

 about nine scales per centimeter, each scale subtended by three hairs, 

 scarcely longer than the scales. 



Skull and teeth. — The skull is longer and relatively narrower, temporal 

 headings less lyrate, rostrum more slender than that of R. firmus. It is 

 much smaller than that of R. victor. X In general characteristics it does 

 not seem essentially different from that of 22. validus. The teeth of R. 

 virtus are not essentially different from those of Rattus firmus and R. victor, 

 but are strikingly different from those of R. validus in being much nar- 

 rowed and in lacking some small extra cusps on the outside of the upper 

 toothrow. 



Measurements. — Head and body, 250 mm.; tail, 278; hind foot, 50; 

 condylobasal length, 61.6; zygomatic width, 26.4; width of braincase, 

 19.3; maxillary toothrow, 10.1. 



Specimens examined. — One, the type. 



* Proc. Acad. Nat. Sci. Phila., 1902. p. 155, June 11, 1902. 



t Proc. Biol. Soc. Wash., vol. 13. p. 141, April 21, 1900. 



X Miller, Smiths. Misc. Coll., vol. 61, no. 21, p. 16, December 29, 1913. 



