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Show 848 ON THE RODENT GENUS HETEROCEPHALUS. [Nov. 17, similar; but the lower jaw of the type of that species has unfortunately been lost. . ,, The incisors, as in the allied genera, project nearly horizontally forward ; and their anterior faces are somewhat flattened and bevelled on their interior halves, so that, as they wear down, the resulting edge of the two incisors combined is more or less W-shaped, but with the outer arms of the W very much shorter than the inner. Externally I can find no specific differences whatever, except in the greater size of the hind feet of H. glaber. It must, however, be remembered that in such a genus as Heterocephalus, m which there are neither ear-conchs, to vary in shape and size, nor hairs, to vary in colour and length, and where there is only one possible manner of life, there is very little room for the ordinary forms of specific variation as found in other genera of mammals. The measurements of the type specimens of the two species are as follows :- Head and body .. Tail Hind foot Forearm and hand Head Muzzle to ear . . Muzzle to eye .. Eye to ear H. phillipsi ( 5 in spirit). mm. 80 35 16*6 21*0 21*5 15*2 7*0 7*0 H. glaber (stuffed). mm. (c) 95 39 21*2 (c) 20*0 Skulls :- H. phillipsi. H. glaber. Occiput to tip of nasals 16*1 21*5 Occiput to tip of incisors 19*4 26*4 Basal length1 16*0 21*5 Greatest breadth 13*6 18*3 Brain-case, length 9*2 11*0 Brain-case, breadth 9*4 12*0 Nasals, length 5*1 7*8 Nasals, breadth 3*2 • 4*4 Interorbital breadth ; 5*1 6*0 Back of incisors torn1 5*7 80 Palatine foramina 1*1 2*3 Palatine foramina to posterior nares 4*0 6*1 Basi-cranial axis 6*1 - Palate, length 9*1 13*6 Palate, breadth outside m 2 4'3 5*0 Palate, breadth inside m2 ....... . 1*5 2*2 Palate, least breadth inside molars . 1*2 1*3 Incisors, breadth 2*1 2*9 Incisors, length 3*9 5*4 1 From basion |