1897.] MALAGASY GENUS BRACHIUllOMYS. 699 



examination shows that the Bhizomijes {Tachyoryctes, Hhizomys) 

 and Brachyuromys are nearly related to each other — the same 

 holds good, in a somewhat minor degree, with regard to Spalax 

 and Siphneus. The Rhizomyes are highly adapted to fossorial 

 habits ; Brachyuromys much less. The molars o£ both will be 

 considered below. 



The skull of the two (Rhizomyes and Brachyuromys) presents 

 the following agreements, B. ramirohitra being somewhat inter- 

 mediate between Tachyoryctes and B. betsileoensis, although standing 

 of course closer to the latter :— 



(1) The zygomata diverge outwards posteriorly, more in Rhi- 

 zomyes than in Brachyuromys ; the malar process of the squamosal 

 parts at right angles from the skull and is strongly developed. 



(2) The jugal is very strong and approaches closer to the 

 lachrymal than in other Muridae. 



(3) The infraorbital foramen in Brachyuromys is situated 

 higher above the molar series and reaches higher up than in other 

 Muridse ; the narrowed lower portion being lower and wider in 

 B. ramirohitra. In Tachyoryctes it is located higher still, and 

 there is almost no narrowed passage below. In Rhizomys the 

 foramen is situated higher still, and much shortened as well as 

 broadened. 



(4) The skulls of both Rhizomyes and Brachyuromys are depressed 

 and massive. 



(•5) MandibulsB short, massive and high. Anterior margin of 

 coronoid process almost vertical. 



(6) The lower maxillary border, between premaxillary suture 

 and first molar, viewed in profile, appears higher anteriorly, sloping 

 down backwards towards the anterior alveolar border. 



(7) The molar series diverge backwards. 



(8) The glenoid fossa is, outside and inside, delimited by longi- 

 tudinal parallel crests. 



(9) The anterior margin of the nasals does not reach as much 

 forwards as that of the premaxillaries. 



The skuU of Rhizomyes differs from Brachyuromys in the following 

 characters, which are all of them the expression of the higher 

 fossorial adaptation and the more hypselodont molars : — 



Eyes and ears very small ; tail very short. 



A sagittal crest. Increase in vertical extent of the maxilla, 

 upwards as well as downwards. — Anterior narial aperture de- 

 pressed and broad. — Foramina incisiva small and situated back- 

 wards, being overgrown by the premaxillaries. The upper 

 posterior processes of the premaxillaries extend also far back- 

 wards. — The distance between m.l and anterior extremity of the 

 premaxillaries, depending on the increased length of the incisor 

 alveoli, is much increased as well. — Viewed in profile, the sloping 

 backwards of the inferior border of premaxillary and maxillary, 

 between the incisors and first molar, is much steeper than in 

 Brachyuromys. — The great horizontal extension of the lower 

 incisors and the great vertical extension of the lower molars 



