98 Dr. J. E. Gray on Species of Chelymys from Australia. 



IX. — On the Species of Chelymys from Australia, with the De- 

 scription of a new Species. By Dr. J. E. Gray, F.R.S. 



In establishing this genus, the only species then known had a 

 distinct nuchal plate, and the existence of this plate is made part 

 of the generic character. We have since received two specimens 

 of the shell of a Tortoise, without the animals, which has all the 

 other characters and appearance of the genus, but is destitute of 

 the nuchal shield ; so I am inclined to amend the generic cha- 

 racters by leaving out this particular, and to use the presence 

 or non-existence of the nuchal shield as a sectional or specific 

 character ; and we have received other specimens of the species 

 with the nuchal shield, which have further illustrated the spe- 

 cies, and show that this shield is always present in it. 

 The species will then stand thus : — 



* Nuchal shield broad and well developed J hinder margin entire. 

 1. Chelymys Macquaria, Gray, Cat. Shield Ueptiles, 57. 



This animal presents two varieties, differing in the height of 

 the back and the width of the hinder marginal shields. Speci- 

 mens brought by the same collectors, probably from the same 

 locality, offer considerable variation in this respect, and appear 

 to form a series of gradations from one variety to the other. 

 The higher and more solid specimens are of the smallest size; 

 but we have very depressed broad margins in the young speci- 

 mens as well as the more adult ones, the latter being twice the 

 size. 



The solid, higher varieties may be only of different sexes, or 

 they may even prove to be species when more is known of their 

 habitation and habits ; indeed I should be inclined to consider 

 them so now if we had not received both varieties from Capt. 

 W. Chambers and Mr. Cuming as coming from the same locahty. 



They vary considerably in the form of the gular shield : in 

 the small, solid, high-shelled variety it is broad and short ; in 

 some of the older of the larger depressed specimens it is equally 

 short and broad ; in the younger depressed specimens it is nar- 

 row, linear elongate. 



** Nuchal shield none j hinder margin dentated. 



2. Chelymys dent at a. 



Shell ovate, wider behind ; hinder margin dentated ; side edge 

 revolute. Nuchal shield none. Back with a slight nodule at 

 the hinder part of the vertebral shields. The first vertebral 

 shield broader than long, the rest longer than broad; the fourth 

 the longest, rather urn-shaped, the margin shelving. 



Younger shell : back slightly keeled ; the margin more ex- 



