284 On new African MarnmaJs. 



Length of nasals 9 ; interorbital breadth 42 ; lengtli of 

 upper molar series 4*1. 



Hab. Kakamega Forest, Kisumu, British East Africa. 

 Alt. 4500'. 



Type. B.M. no. 6. 5. 6. 5. Collected and presented by 

 F. VV. Isaac, Esq. 



Readily distinguishable by its abruptly grey head, parti- 

 coloured feet, and the conspicuous buffy lines down each side 

 of its belly. 



Desmomys, gen. nov. 



External characters and general shape of skull as in 

 Pelomys and Mylomys, but molars of a structure approaching 

 that found in CEnomys. 



Proportions and general external appearance about as in 

 Pelomys. Pollex minute, with a rudimentary nail ; fifth 

 fore toe either with a very short claw (dembeensis) or a nail 

 (harringtoni). Fifth hind toe little longer than the hallux. 



Skull of the peculiar shape, short-muzzled and bowed 

 above, characteristic of Arvicanthis, Pelomys, and Mylomys, 

 quite different to the long flattened skull of CEnomys. 



Incisors faintly and inconspicuously grooved, equally 

 different from the strongly grooved incisors of Pelomys and 

 Mylomys, and the smooth convex ones of Arvicanthis and 

 CEnomys. 



Molars, while not so extreme, yet showing a strong re- 

 semblance to those of CEnomys. The cusps are not so high, 

 but there is a similar tendency to the development of tine 

 enamel ridges running backwards from the main cusps in the 

 line of the tooth-row, and tending to obliterate the essential 

 laminate structure. From this it results that certain cusps, 

 notably the postero-external and postero-internal, of both in x 

 and m 2 , instead of being roughly circular in section as in 

 Pelomys, are almost " guttate " (Ridgway, pi. xiv. fig. 8), 

 with a long pointed angle behind. Lower molars with the 

 cusps directed forwards somewhat as in Mylomys; second 

 lamina of m z little narrower than the anterior lamina, strongly 

 notched posteriorly, so as to form two cusps, of which the 

 inner is rather the larger. 



Type. D. harringtoni (Pelomys harringtoni, Thos.). 

 Other species — Mus dtmbeensis, Riipp. 

 The species for which I now propose a special genus have 

 always been a puzzle, and den.beensis has in turn been referred 

 to Mus, Arvicanthis, Golunda, Pelomys, and CEnomys. They 

 combine in a curious way the general characters of Pelomys 

 with a tendency to the peculiar tooth-structure of CEnomys, 

 to which they have no resemblance in other respects. 



