THE 



GEOLOGICAL MAGAZINE. 



NEW SERIES. DECADE V. VOL. V. 



No. III. — MARCH, 1908. 



OE,IGrIlSr.A.ll. .A.I?,TICLEIS. 



I. — A. Giant Sub-Fossil Rat froji Madagascar, Myobyctes eapeto,^ 



gen. et sp. no v. 



By Dr. C. I. Foksyth Major, F.Z.S. 



AMONGST the vertebrate remains which I found in the marshes of 

 Sirabe (Central Madagascar), a large Rodent is represented by- 

 two right ossa innominata, one of which (B.M. M 7o85) is fairly- 

 complete, only the free portion of the pars dorsalis of the ischium 

 being broken ofE. 



The very elongate, comparatively narrow ilium, divided pretty- 

 equally by the crista lateralis into a dorsal and a ventral portion, 

 shows that we have to deal with a muriform member of the Rodentia; 

 it comes very near in its general form to the same bone of the Malagasy 

 genera of rats Nesomys, Gymnuromys, Eliurus^ and Hypogeomys ; in 

 Brachyuromys the long axis of the ilium is more straightened. The 

 single tuberculum iliopectineum (iliopubicum) for the insertion of the 

 psoas minor is enormous, and the spina ventralis posterior (anterior 

 inferior of man) is likewise very strong. 



The conformation of the os pubis, however, is markedly different 

 from that of the genera above-mentioned ; its pars anterior is very 

 long and directed more decidedly backwards, and the symphysis 

 is quite minute. This is the shape of a vole's pubis, and in a general 

 way of all fossorial Muridse and Rodents generally,^ so that 1 do not 

 hesitate in assigning the fossil to a highly fossorial Rodent. 



The length of the fossil innominatum is 134"5mm. ; that of the 

 bone in a Nesomys rufus-=. 41 mm. ; the skull of the latter has a 

 basal length of 39-5mm., the absolute maximum length — front of 

 nasals to occiput — being 49 mm. The approximate corresponding 

 measurements of the cranium of the new genus may therefore be 



1 rapeto is the Malagasy word for ' giant, uncanny.' 



- Cf. in TuUberg, '" iJber das System der Nagethiere" (1899), the figure of the 

 innominatum of Nesomys (pi. 32, figs. 11, 12), and those of the genera of fossorial 

 Eodents, viz., Spalax (figs. 13, 14), Ellobius (figs. 15, 16), Arvicola ampMMus 

 (figs. 17, 18), Uesperoimjs (figs. 19, 20), Geomys\figs. 27, 28), GeorycJms (pi. 31, 

 figs. 1, 2), Ctenomys (figs. 19, 20), Haphdon (pi. 33, fig. 8), Ferodipus (figs. 23, 24). 



DECADE Y. — VOL. V. — NO. III. 7 



