•.234 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.58. 



ing on to the braincase — very different from the broadly divergent 

 ridges of typical Rhipidomys. Zygomatic plate narrow, with ver- 

 tical front edge, little projected forwards. Palatal foramina ending 

 level with the front of m^. Molars rather small in proportion to the 

 size of the skull, conspicuously smaller than in the species of the 

 T. aureus group. 



Dimensions of the type: Head and body, 128; tail, 155; hindfoot, 

 27; ear, 18.5. Skull — greatest' length, 33; condylo-incisive length, 

 '30; zygomatic breadth, 17.4; nasals, 12; interorbital breadth, 4.2; 

 breadth of braincase, 14; palatilar length, 13; palatal foramina, 7.1; 

 post-foram.inal palate, 4.6; upper molar series, 4.6. 



Type. — Aclule male from Torontoy, U.S.N.M. No. 194548; original 

 number 173. Collected May 15, 1915. 

 Seven specimens, as follows: 



Torontoy, 9,500 feet, 6 (Nos. 194547-8, 184894-7). 

 Machu Picchii, 8,000 feet, 1 (No. 194898). 



From the point of view of systematic arrangement this well- 

 marked species presents a problem of considerable difficulty; for with 

 the general skull shape of the less typical species of the genus 

 Thomasomys^ it has comparatively broad feet, showing that it is a 

 climbing animal ; and it is just the broad feet which are supposed to 

 characterize the members of Rhipidomys., while those of Thomas- 

 omys, more or less ground living, have long narrow feet. Moreover, 

 the doubt as to its proper generic position is complicated by the fact 

 that, while the more strongly marked species of Rhipidomys have 

 broadly divergent supraorbital ridges, this can not be said of all 

 of those which have been included in the genus. 



40. THOMASOMYS GRACILIS Thomas. 



1917. Thomasomys gracilis Thojias, Smiths. Misc. Coll., vol. 68, No. 4, p. 2. 

 April 10, 1917. 



A very small species allied to T. boeops. 



Size about the smallest of the genus. General appearance very 

 much as in T. hoeops or a miniature T. notatus. Color above dark 

 grayish buffy or clay color (approximately "Dresden brown" of 

 Ridgway), the posterior median area usually darker, the darkening 

 not defined enough to be called a stripe. In some specimens the 

 color varies toward cinnamon, but it is not clear whether this varia- 

 tion is seasonal or individual. Undersurface soiled grayish buffy, 

 not sharply contrasted; the hairs slaty basally, dull pinkish buff 

 terminally. Ears fairly large, blackish, contrasting with the gen- 

 eral color of the head; a small patch behind their lower bases pale 

 buffy. Hands and feet with brown metapodials and light digits. 

 Tail long, well haired, blackish brown, scarcely lighter below; the 

 extreme tip sometimes white. 



