the Genus Oricetomys. 287 



In addition to the type we have from Zanzibar three speci- 

 mens collected by Mr. J. T. Last and an adult male collected 

 and presented by Dr. Aders. 



Description. — Apart from its larger size this species is 

 very similar in outward appearance to C. emini set net us, just 

 described. The fur is short and thin, but quite soft and 

 sleek. In four of the specimens, including the type, the 

 general colour of (he back ranges from russet or cinnamon 

 to mummy-brown ; but one sent by Dr. Aders is consider- 

 ably darker. There is no distinct trace of mid-dorsal 

 darkening in any. The underparts are thinly clothed with 

 pure white or yellowish hairs. The ears are brown, nearly 

 matching the dorsal colour. The hands are whitish in colour 

 from the wrists. The feet are dark brown above, with the 

 dio its and inner margins whitish. The terminal half of the 

 tail is white. 



The skull is about as large as in emini (condylo-basal 

 length 68-73'3 mm.), and considerably larger than in 

 gambianus ; it agrees with that of emini further in its 

 relatively small zygomatic breadth ; this dimension expressed 

 as a percentage of the condylo-basal length ranges between 

 46'7 and 47*8 in cosensi, 45 - 4-47'8 in emini, and 49-525 in 

 gimbiauus. The anterior palatal foramina are relatively 

 larger than in emini, their lengths ranging between 12"5 and 

 14*2 °/o °f the condylo-basal length instead of between 9'8 

 and 13-4 °/ , and the breadth 4'9-6'2 °/ instead of 4-3-4-8 %. 

 In other respects the skull agrees with that of emini. 



Collectors measurements of type (with dimensions of Dr. Aders's speci- 

 men in brackets). — Head and bodv 343 (369) mm. ; tail 390 (381) ; hind 

 foot 70 (72) ; ear 41. 



Measurements of skull of type (with those of Dr. Aders's specimen in 

 brackets).— Condylo-basal length 72 (733) ; zygomatic breadth 336 

 (34-7) ; interorbital constriction ll - 3 (10"6); mastoid breadth 25*1 (25-1); 

 nasals 31 x 10 (333 X 10) ; incisor to m. 3 39-8 (407) ; diastema 24-2 

 (24-7) ; length of anterior palatal foramina 10 - 2 (97) ; length of pre- 

 orbital fossa for masseter medialis 14 - 4 (14 5); least diameter of 

 zygomatic plate 6"3 (5'3) ; molar crowns 107 (107). 



Remarks. — The Zanzibar Cricetomys is of quite excep- 

 tional interest, and I have much pleasure in naming it after 

 Colonel Cosens, who is most generously finding the funds for 

 Mr. Swinny's collecting work. The nearest geographical 

 allies of C. cosensi are the mainland forms named by Heller 

 C. g. enguvi and C. g. osgoodi ; but these in common with 

 the numerous mountain races described from East Africa 

 are animals of a wholly different type. They resemble 

 gamb'nnus, as well as the southern subspecies viator, cunctator. 



21* 



