OBSERVATIONS ON THE RODENTIA. 277 



a more elongated form, and the facial portion is proportion- 

 ately larger as compared with that devoted to the protection 

 of the brain. One of the most striking characters observable 

 in the crania of the Muridae, consists in the peculiar thin 

 plate which is produced anteriorly from the zygomatic pro- 

 cess of the maxilla. This thin plate (see a, fig. 34, and d, 

 fig. 35) is usually of considerable extent, and is sometimes 

 nearly vertical (as in Gerbillus Indicus, fig. 35, d), but is ge- 

 nerally carried upwards and outwards from the palate, as in 

 the common rat {Mus decumanus). This plate is proportion- 

 ately most extended in the species of Gerbillus just men- 

 tioned, but in other species of the same genus it is very 

 short ; this is the case in Gerb. brevicaudatus (fig. 35, c)i 

 Gerb. otarius, Gerb. pygargus, &C. 1 In the hamster {Cri- 

 cetus vulgaris) its outer surface is concave, and in Neotoma 

 Floridana it is also concave, though in a less degree. Cri- 

 cetus auratus 2 (fig. 35, e and /) is remarkable for the nar- 

 rowness of this process of the maxilla. In this animal it 

 does not project so as to protect the opening beneath, which 

 leads into the nasal cavity, as in nearly all the other species 

 of th e Muridw which I have examined. In Hydromys 

 chrysogasler there is a still narrower loop of bone inclosing 

 the ant-orbital foramen, which is larger than usual, and 

 there is a remarkable angular process projecting from the low- 

 er and anterior portion of this loop. 



The two animals just mentioned {Cricetus auratus and 

 Hydromys clirysogaster), and the Rhizomys Sinensis of Mr. 

 Gray (which is the Nyctocleptes Dekan of M. Temminck), 

 constitute the only species of the present family, the skulls 

 of which I have examined, in which the thin plate arising 

 from the maxilla above described is not produced anteriorly, 

 as we find it in the rat. 



Judging from the figure of the skull of Nyctocleptes Dekan 

 given by Temminck in his ' Monographies, ' I feel but little 

 doubt that this animal belongs to the present family ; it offers 

 however some marked exceptions to the general characters of 

 the crania of the Muridce: the most remarkable of these is the 

 want of the thin plate of the maxilla just mentioned, and the 

 absence of the vertical slit through which (in the genus Mus) 



1 See M. F. Cuvier's 'Memoire sur les Gerboises et les Gerbilles,' pub- 

 lished in the ' Transactions of the Zool. Society,' vol. ii. pt. 2, plr25 & 26. 



2 A beautiful new species of hamster, from Aleppo, recently described by 

 me, and to which I have applied the above specific name, on account of its 

 rich yellow colouring ; the under parts of the body, however, are nearly 

 white. The length, measured in a straight line, is 6^ inches, the ears are 

 about i an inch long, and the tail is about the same length 



2f3 



