CRANIAL CHARACTERS OF THE SXAKE-RAT. 



67 



Brown Rat (2fus decumanus), which is quite different. If there- 

 fore the new rat is a mere variety of either of the two species 

 which have been long known as members of the British mamma- 

 lian fauna, and which have always been considered specifically 

 distinct, it must be deemed a variety of Mus rattus ; but I claim 

 for it distinctive characters separating it from that rat, quite as 

 marked as those which distinguish the Brown from the old English 

 Black Bat. Indeed Mus decumanus more nearly resembles Mus 

 rattus than does the new rat. It was suggested to me, at the 

 time I exhibited the living specimens, that an appeal must be 

 made to the cranial characters of each, before the distinctness and 

 the degree of distinctness between the two could be established. 

 The result of this investigation I now give to the Society. 



On the table are the skulls of the identical rats that were for- 

 merly exhibited — two adult males ; and I have also some enlarged 

 outline drawings (from which the accompanying woodcuts were 

 taken) showing the salient peculiarities of each cranium. The 

 Fig. 1. Fig. 2. 



Top view of Cranium of Snake-Rat. 

 Enlarged two diameter-* 



Top view of Cranium of Mus rattus. 

 Enlarged two diameters. 



5* 



