1907.] Dr- Hossack : The Rats of Calcutta. ■ 33 



but Anderson, who originally worked out the genus, says nothing about this character 

 in his description of the incisors, while Gray, who laid the foundations for Anderson's 

 work, says definitely that in his type, Nesokia {Mus) hardwickii, the incisors are fiat 

 and smooth. Personally I have found the incisors covered with fine, irregularly 

 parallel markings, but these are not more marked in Nesokia than in M. decumanus 

 or any other form of Mus examined, whether in my own or in the Indian Museum 

 collection. 



Gray made the transverse lamination of the molars the principal generic difference, 

 but Anderson makes the cranial characters of greater importance, on the ground 

 that in the young Nesokia skull the characters of the molars approximate to Mus. 

 The fact is that although the adult worn teeth of Nesokia are very clearly distinguished 

 from those of Mus by their larger size and bulk, and the possession of straight instead 

 of sinuous laminae, the young unworn tooth is very similarly constituted in both. As 

 will be seen in figure 52, the cusps of an unworn lamina may be nearly as distinct in 

 Nesokia as in Mus. The cusps are, however, very soon lost, and then the transverse 

 laminae become very distinct, so distinct that they are never lost, even in a very much 

 worn tooth. It escapes the stage often seen in an old M. decumanus of being reduced 

 to a featureless surface of dentine. 



Additional rudimentary lamines or cusps. — Whereas in Mus as typified in M. rattus 

 and M. decumanus, additional cusps or laminae are habitually found, in A^. bengalensis 

 they are frequently absent altogether, or are represented only by a minute trace, and 

 that sometimes only on the teeth of one side. In fig. 52 the inside cusp, representing 

 a third lamina in the second and third molar, is very well marked, but it is frequently 

 represented by a trace so small that it is difficult to represent it in an illustration. In 

 eight immature skulls ex:amined, the second upper molar showed a well marked, addi- 

 tional rudimentary lamina on both sides in four instances, in two instances there was a 

 trace of it on the right side only, and in two instances there was no trace at all. The 

 third molar in the same series showed it well marked on both sides only in one instance. 

 In two there were traces on both sides, and in one a trace on the left side only, while 

 half of them showed no trace of it at all. In mature skulls it is practically lost al- 

 together in the third molar, only one, out of twenty examined, showing it at all. It 

 can still be made out in the second molar in five out of twenty. In five there was 

 only a faint trace of it, sometimes on one side only, and in ten no trace could be found 

 at all. 



Lower molars. — Occasionally there is found in the second lower molar a third 

 rudimentary lamina or a trace of one, but it is notable that it is always found on the 

 external side of the tooth as against the inside of the upper molars. The mesial addi- 

 tional laminae found in Mus are not found in this Nesokia, though present in the 

 only young specimen of Bandicoot which I have obtained. 



Skull. — The skull is very different in general appearance from that of Mus. It is 

 a very broad, heavy, blunt-nosed skull with a globular cranium, while the whole skull 

 shows a depth and solidity that are never found in Mus. The pterygoids are very thin 

 and high, and the pterygoid fossae deep (broken in skull figured). The auditory 



