556 MR. G. A. BOULENGER ON EMYS BLANDINGII. [June 23, 



its length (from the extremity of the plastron) being contained twice 

 and two thirds in the length of the shell in the adult male, and four 

 times in the adult female ; in the quite young, figured by Agassiz, 

 about once and a half. In the adult male of E. orbicularis the 

 length of the tail is contained about once and a half in the length of 

 the shell, in the female twice to twice and one fourth ; in the quite 

 young, tail and shell are of equal length. I count 27 caudal vertebrae 

 in the skeleton of E. blandingii (adult female) in the Museum, and 

 3 1 in a skeleton of a female E. orbicularis. 



Other differences are to be found in the coloration of the head, 

 the lower jaw and throat being of a uniform yellow colour, contrasting 

 with the dark brown of the upper jaw ; and in the colour of the 

 iris. This is of a bronzy brown in the female and reddish brown in 

 the male. Similar sexual variations in the colour of the iris are 

 known to occur in Cistudo Carolina. In the newly-born Emys 

 orbicularis the -iris is of a uniform dark brown ; as the animal 

 advances in age small round yellow spots, similar to those on the 

 sides of the head, appear on the iris, and gradually increase in size 

 until, in the adult, the iris is principally, or even entirely, yellow. 



A few words as to the habits, so far as I have been able to observe 

 from the two specimens lent me by the Society, and which I kept 

 for a couple of weeks in company with specimens of the European 

 species. Holbrook says, " It is known to be a land animal, and 

 found about the meadows and prairies of the West." I am not able 

 to confirm the statement that it is terrestrial. The Society's specimens 

 go to the water, though less readily than their European congeners ; 

 they dive and feed in the water. When disturbed on land they 

 usually seek shelter by withdrawing into the shell, as do Land- 

 Tortoises ; whilst E. orbicularis, under similar circumstances, makes 

 for the water. When handled, the timid E. blandingii nearly 

 always retires into the shell, whilst even fresh-caught specimens of 

 E. orbicularis seldom do so. 



To conclude, it may be observed that, though belonging unques- 

 tionably to the same group as E. orbicularis, E. blandingii shows in 

 some of its characters, shorter tail and coloration of the iris, as well 

 as in its less aquatic habits, a certain approach to its American 

 allies of the terrestrial genus Cistudo. 



EXPLA]yf ATION OF PLATE L. 



Fig. 1. Emys blandingii, Holbr. 



1 a. Head of male, side view. 



1 h. Ditto, upper view. 



1 c. Ditto, lower view. 



1 d. Head of female, side view. 



1 e. Skull of female, upper view. 



1 /. Ditto, side view. 



1 g. Mandible, lower view. 

 Fig. 2. Emys orbicularis. 



2 a. Head of male, side view. 

 2 b. Ditto, upper view. 



2 <7. Ditto, lower view. 



2 c. Skull of f'em.ale, upper view. 



2/. Ditto, side view. 



2g. Maudible. lower view. 



