1907.] Dr. Hossack: The Rats of Calcutta. 29 



ridge is found, as has been already described in connection with Mus rattus. Where 

 the occipital ridge is very well developed it may give the occiput the appearance of 

 being vertical, but there is always some slope. The zygomatic plate may rarely be 

 nearly perpendicular, but even in the young skull it hardly ever slopes downwards and 

 forwards as it does in young M. rattus. 



Teeth. ^AitQV the very full description given of the teeth oi Mus rattus, there 

 is very little to be said ; those of Mus decumanus are identical except for a slight 

 difference in size, being slightly larger, particularly the incisors. Figure 20 shows 

 well a tooth that is extremely worn so that it has become a mere block of dentine with 

 only a trace of laminar division left, and not even a trace of cusps. The young teeth 

 show the same tendency to be furnished with additional cusps and laminae as is seen 

 in M. rattus, and figure 27 shows particularly well the central additional rudiment- 

 ary laminae of the lower molars. In addition to the antero-internal supplementary 

 lamina or cusp normally present in the second and third molar in M. rattus, there is 

 occasionally found a trace of an antero-external cusp, indicating a tendency of the 

 extra lamina to extend completely across the tooth. This has already been noted 

 by Miller in his description of Mus validus, in which the external cusp is normally 

 present even in the worn tooth and is generally joined to the internal one, complet- 

 ing the additional lamina in the second molar, whereas in the third molar the ele- 

 ments are said to be less distinct : in the figure the two extra cusps are shown quite 

 separate, with no indication of a junction. In four out of twelve young M. decuma- 

 nus skulls I have found this trace of an antero-external cusp, whereas in Mus rattus 

 I have seen it once only. 



NESOKIA BENGALENSIS. 



The Indian Moi.e-Rat. 

 (Synonymy after Blanford.) 



Arvicola hengalensis, Gray and Hardw., 111. Ind. Zool., ii, pi. 21 (1833-34). 



Mus kok, Gray, Charlesworth's Mag. N. H., i, p. 585 (1837). 



Mus (Neotoma) providens, Elliot, Mad.. Jour. I^. S., x, p. 209 (1839). 



Nesokia hardwickii, Kelaart, Prod., p. 65, nee Gray. 



Nesokia kok, Kelaart, ibid., p. 66. 



Mus daccaensis, Tytler, A. M. N. H. (2), xiv, p. 173 (1854). 



Mus tarayensis, plurimammis , and morungensis, Hodgson, Horsfield, A. M. N. H. 

 (2), xvi, p. 112 (1885). 



Nesokia indica, Blyth, J. A. S. B. xxxii, p. 328 ; JerdonMam., p. 187; Theobald, 

 P. A. S. B., 1866, p. 239 ; Blyth, Mam. Birds, Burma, p. 38. 



Mus {Nesokia) indicus, Blyth, Cat., p. 112, partim. 



Mus {Nesokia) hlythianus, barclayanus, and providens, Anderson, J. A. S. B., 

 xlvii, pt. 2, pp. 225-231, pi. xiii. 



Nesokia harclayana, Blanford, Yark. Miss. Mam., p. 46, pi. xa, fig. i (skull). 



