th< Genus Cricetomys. 285 



may he similarly investigated ; but in the case of the 

 temporalis, far greater changes transpire with advancing age 

 than is the case with, the niasseter system. The material 

 before me in the present instance is not rich enough in old 

 skulls to lead to any definite result beyond the fact that the 

 posterior portion of the temporalis is stronger in those forms 

 with a relatively weak masseter medialis than in those in 

 which the latter muscle is more powerfully developed : — 



Incisor to m. 3 = 100 : — 

 Masseter medialis. grahami. olivice. gambianus. dichrurus. 



Length of preorbital fossa 

 for origin of Masseter 

 medialis 31-2 31-34-5 308-37-7 37"3 



Greatest transverse dia- 

 meter of infraorbital 

 canal 265 22-3-257 27-1-29-2 27 



Masseter lateralis. 



Least antero-posterior dia- 

 meter of outer wall of 

 infraorbital canal .... 17-8 16-3-177 14-5-16-4 15-4 



Temporalis. 



Mastoid breadth minus the 

 least distance between 

 temporal ridges behind. 327 312 29"1 28-8 



Collector's measurements of type. — Head and body 300 mm. ; tail 357 ; 

 hind foot 70 ; ear 35 (hind-foot measure merit too large, 65 on skin). 



Measurement of skull. — Condylo-basal length 62-4; zygomatic breadth 

 31-7 ; interorbital constriction 98 ; mastoid breadth 23*4 ; nasals 

 25 2 X 8*8 ; incisor to m. 3 34-3 ; diastema 20 ; length of anterior palatal 

 foramina 5-4 ; length of preorbital fossa for masseter medialis 107 ; 

 least diameter of zygomatic plate 6 - l ; molar crowns 10 - 4. 



2. The emiui or sleek-furred group. 



In the southern part of the tract occupied by C. gambianus 

 and in the forested region to the south of it we meet wilh a 

 number of forms which, if judged by external appearance 

 alone, would all be referred to one single species. The forms 

 in question range from the Gambia, Fernando Po, Gold 

 Coast, and adjoining countries on the west, eastwards and 

 southwards right through the Congo Basin ; they appear also 

 to have an outlying representative in the island of Zanzibar. 

 All are characterized by the possession of soft, sleek, and silky 

 fur, which varies in length and density in different parts of 

 the enormous range indicated. Beneath the uniform coats a 

 great wealth of variation is displayed in the skulls ; and I 



Ann. & Mag. N. Hist. Ser. 9. Vol. iv. 21 



