1900.] Allen, New American Marsupials. 199 



Above dark reddish brown suffused with blackish ; sides lighter and more 

 rufescent ; ventral surface pale buffy white ; nose patch but little lighter than 

 the top of the head ; ocular patch deep black, barely enclosing the eye posteri- 

 orly, and extending as a broad band to the nose ; cheeks pale buff ; ventral 

 surface dull yellowish white ; ears blackish ; feet blackish brown, the toes 

 lighter ; tail rather light brown, darkest proximally on the upper surface, the 

 lower surface and the apical third almost flesh-color. 



Measurements. Type (collector's measurements), total length, 355mm.; 

 head and body, 151 ; tail, 204 ; hind foot, 22 ; ear (in dry skin), 15 x 14. 



Skull long and narrow, zygoma very little expanded ; nasals narrow, very 

 slightly expanded posteriorly ; interorbital region flat, cylindrical ; supraorbital 

 bead very slightly developed, and present only in very old specimens. Total 

 length, 39.5 ; basal length, 36 ; nasals, 19 ; palate, 21 ; zygomatic breadth, 

 20 ; mastoid breadth, 13 ; interorbital breadth, 7.7. 



This species is represented by three specimens, an ' old adult ' 

 male (the type), a ' young adult ' male, and a * young adult ' female. 

 The two males present practically the same measurements ; the 

 female is much smaller than the males, measuring as follows : 

 Total length, 317 ; head and body, 132 ; tail, 185 ; hind foot, 17. 

 The female has no pouch ; three nipples are clearly visible on the 

 left side of the inguinal region ; on the right side the skin is not 

 in good condition. 



Thylamys keaysi is easily recognized by its dusky brown color 

 and very long tail, which is fully one fourth longer than the head 

 and body. Its long, narrow skull, the nearly smooth edges of the 

 interorbital region, and the very slight posterior widening of the 

 nasals seem to ally it more nearly with the Thylamys group than 

 with the typical forms of Marmosa. In coloration it also resem- 

 bles T. carri from Trinidad, but the tone is darker, and it is also 

 a much larger animal. 



