1878.] J. Anderson^O;i the Suh- Genus Nesokia. 219 



those of worn teeth, and that they do not contain the characters of the 

 dentition as seen in the teeth before they are worn. In the latter condition, 

 each of the three laminae of the first upper molar presents a large central 

 cusp, and a much smaller or even minute cusp on either of its sides, resulting 

 as it were from the sinuous characters of each lamina of the tooth. In true 

 mice and ordinary rats, the laminae are transversely more sinuous and 

 smaller, whereas in JVesokia they are large and transverse without any 

 marked sinuosity, in the more typical forms. In the second upper molar, 

 there are only two laminae, the first being abortive and only represented 

 by a small isolated cusp attached to the anterior face of the inner cusp or 

 fold of the first of the two laminae, which is exactly the same arrangement 

 as in Mus. The last molar, except in having its laminae more regularly 

 transverse than in 3£tcs, resembles the same tooth in this latter genus. In 

 the lower jaw, there is the same regularly transverse character in the larger 

 laminae as compared with Mus, but all the cusps are the same. In the 

 large rats of the type of 31. giganteus, Hardwicke, the teeth conform more 

 to the type characteristic of the ordinary rats and mice, the laminae, how- 

 ever, being relatively larger than in Mus and less sinuous, but taking the 

 dentition as a whole, in connection with the form of the skull, these large 

 rats are more closely allied to Nesokia than to the true rats, an opinion 

 which was first held by Sir Walter Elliot.* 



The incisor teeth of a Nesolcia are always broader than those of an 

 ordinary rat, and in this respect are more chisel-shaped, but the incisor 

 teeth of the large rats such as M. giganteus are also proportionally broader 

 than those of ordinary rats. 



In the adult animal, such as that figured by Prof. Peters, the laminae 

 are very regularly transversely oblong witho^t any trace of such cusps as 

 those I have described ; and in old individuals of the larger rats, such as M. 

 gigchoteus, the teeth I have observed to be worn down, much in the same 

 way as in the so-called Nesolcia = Spalacomys. Considering these facts, 

 it does not appear that the genus Nesokia has any ground to recognition 

 on characters derived from the dentition. The points in which the skulls 

 of rats referable to the type of M. (Nesokia) hardwickii, Gray, (Spala- 

 corny s indica, Peters,) differ from those of the ordinary rats and mice are, on 

 the other hand, much more pronounced than any difference in their dentition. 

 The skull of Nesokia is a much broader and shorter skull with a short stout 

 muzzle and expanded zygomata. The brain case is much shorter and broader 

 than that of any member of the genus 3Iiis. The temporo-parietal ridges also 

 are proportionally nearer each other than in Mus, and the upper surface of 

 the parietals is more flattened. The anterior palatine foramina are much 



* Madr. Joum. Lit. and Sc, ^^ol. X, p. 209. Sir W. Elliot erroneously regarded 

 M. providens and M. (jigantetis as belonging to the genus Neotonia. 



