00 OBSERVATIONS ON THE RODENTIA. 



upwards, passing between (he caudal seta and terminating in acute points : 

 the legs are very long and slender : the insect is of a dark brown colour, 

 the wings being opaque, dark brown, and the exterior portion of the fore 

 wings regularly spotted with dirty white ; the hind wings are immaculate ; 

 the pro- and mesofcmora having a bright testaceous ring ; the metafemora 

 are testaceous, with the apex only dark brown, the tibia are rather paler, 

 and the tarsi nearly black. 



Inhabits Van Dieman's Land. There is a single specimen 



in the cabinet of the Rev. F. W. Hope'™ ™' { ^< 



I bnn ^IimBt eno m hs^aans od jagim usi 



.TOffronfi 



•d? "tools ;ni£ 10 Joohoq oifa Q~A&i owli iO ' 



Art. VIT. — Observations on the Rodentia, with a view to point out 

 the groups, as indicated by the structure of the Crania, in this or- 

 der of Mammals. By G. R. Waterhouse, Esq., Curator to the 



Zoological Society. 



The various published classifications of the Rodentia appear 

 to be chiefly founded upon the external structureof the species 

 composing this order, combined with their dentition. The 

 habits of animals of the same group, however, are often very 

 variable, and their external characters and certain portions 

 of their skeletons, are of necessity equally so. " The skele- 

 tons of Rodentia" says Cuvier, 1 "are so variable, owing to 

 the diversity of the movements of the species of different ge- 

 nera, and to the presence or absence of clavicles, that it is 

 difficult to find any characters in common, unless it be in the 

 bones of the skull." These considerations have led me to 

 search in the skull for characters by which to define the 

 larger groups and to determine the affinities of the genera, 

 and the object of the present communication is to point out 

 such as appear most important, and in fact to state the re- 

 sults arising from the examination of an extensive series of 

 crania, with the view of so arranging the various species of 

 rodents, that by the position of any particular individual the 

 most important points in its structure shall be indicated, and 

 the relative value of the characters expressed by the nature 

 of the divisions and sub-divisions. 



It may be asked upon what principles I estimate the value 

 of characters ? and as this is a very important point, a few 

 words on this subject appear necessary. I may answer that 

 I value a character by its constancy ; and consider that cha- 

 racter of most importance which extends through the greatest 

 number of species, provided these species evince affinities one 

 with another by the gradual modifications of other characters 

 of less importance, — that is to say, more subject to variation. 



1 ' Ossements Fossiles.' 



