new Species of Mastacomys. 551 



one imiiifidire spociinen from Victoria, aiul some cave- 

 remains from Xew South Wales*. 



Tiio Victorian and Now South Wales specimens are liotli 

 of just about the same size as the original Tasmanian 

 example. 



But the Soutii-Australian one is considerably smaller, and 

 obviously of a dilferent species. It may be called 



Mastacomj/s mordicuSj sp. n. 



Size, as gauged by teefh, only about three-fourths of tliat 

 of M. fuscus. Teeth quite similar iu structure to those of 

 that anin)al. 



Skull apparently lower in proportion, at least anteriorly, 

 tiie zygomatic plate measuring in heigiit only about 5*7 mm. 

 from the upper bridge to the lower edge of the foramen, 

 while in the type of fuscus this measurement is 6'9 mm. 

 Anterior edge of plate deeply and abruptly cut out to a depth 

 equal to half its height, that o( fuscus only evenly but slightly 

 concave. 



The molar roots are as follows : — M^, a large antero- 

 external, a small postero-external, and two smaller inner, 

 near together, therefore four in all ; m^, four subequal roots, 

 j)laced in a square ; w*^, three roots, two large anterior level 

 with each other, and a large median posterior. This arrange- 

 ment is not at all bke that of any of the forms illustrated in 

 Prof. Wood-Jones's recent paper on the subject. 



Length of the molar tooth-row, alveolar 9'1 mm., grinding- 

 suiface (unworn) 7"2 (respectively lO'i and 8*5 mm. in 

 JJ. fuscus) ; greatest breadth of w^ 3'0. 



J Jab. Mt. Ganibier district, S. Australia. Type from a 

 guano-cave. 



Ti/pe. A right maxilla, with the tliro:3 molars. 13 31. 

 no. 22. 10. 1. 3. Presented by Prof. F. Wood-Jones. 



While the Eastern forms from New S )uth Wales and 

 Tasmania are all of about the same size, this South-Australian 

 .species is readily distinguishable by its much smaller 

 dimensions. 



Whether it is still to be numbered among the recent fauna 

 of South Australia remains to be proved. 



* The specimens from Central Au.striilia referred by >[r. Waite (Zool. 

 Horn K.\p. p. 400, fig-. (5, LsiX!) to Mtidiuinuyn would seem to be either 

 liuttua or Pseuiloinys, The moliirs are not broad enough in proportion 

 to tlieir lenj^th for those of Mastacomys. 



