86 Dr. J. E. Gray on Trionjx Phayrei. 



opinion on the form wliich the callosities found on a young 

 specimen will assume when it becomes adult ; and I never 

 saw a lateral linear callosity like that of Dogama, which Mr. 

 Theobald says his species possesses, become a broad callosity, 

 dilated at each end like that figured by Dr. Anderson ; and 

 Mr. Theobald does not mention any anal callosities as found 

 in his specimen, which we must recollect, from its size and the 

 state of its coloration, must have been half-grown, if not an 

 adult animal. And therefore I cannot believe that it would 

 have the large triangular anal callosities occurring in Dr. An- 

 derson's figure. Species that have such a callosity generally 

 have a small circular callosity even in their youngest state ; 

 and therefore I conclude, from all these characters, that the 

 Trionyx Phayrei of Dr. Anderson has no affinity with the 

 animal described under that name by Mr. Theobald. 



Dr. Anderson objects to the genus Sciurus being separated 

 into genera by organic characters, such as the shape of the 

 skull and the pencilling of the ears (Proc. Zool. Soc. 1871, 

 p. 139), but prefers dividing them, according to their colouring, 

 into lineated grizzled squirrels and dorsal lineated squirrels, 

 and lateral lineated squirrels and ventrilineated or (as he 

 calls it in another place) belly-banded squirrels. To my 

 mind this is a retrograde movement rather than an advance in 

 zoological science. I see no objection to a man refusing to 

 adopt the new generic names ; but when a genus has been 

 divided by organic characters founded on the examination of 

 a large series of species, including a large collection of speci- 

 mens, it certainly is an advantage to use those divisions as 

 sections of a genus, or at least to take care, in describing the 

 species, that the characters on which these divisions are 

 founded are carefully examined and fully described. If Mr. 

 Theobald and Dr. Anderson had availed themselves of the 

 characters afforded by the skulls and the development of the 

 callosities of the mud or three-toed tortoises, and had referred 

 the specimens they described to the sections so proposed 

 (although they did not adopt the genera or subgenera), they 

 would not have left the species they described in such doubt, 

 or they would not have referred two species so evidently un- 

 like to the same name. But then I know that it is not easy 

 to do this when the describer depends on Indian drawings for 

 his materials. I can only understand Dr. Anderson's remarks 

 on the species of squirrels by his attention being confined 

 to external appearances as represented in figures ; and we 

 may judge of the kind of inartistic figures he has to work 

 from by the plate of Sciurus quinquestriatus which he has* 

 published (Proc. Zool. Soc. 1871, pi. 10). 



