262 
DR. A. GUNTHER ON GIGANTIC LAND-TORTOISES. 
thin, in some parts quite transparent*. There is almost a total absence of anterior 
declivity of the first dorsal scute, its front margin being but very little below the level 
of the highest point of the carapace. The sides of this fore part of the carapace are 
expanded, not contracted as in T. ephipjgium. The caudal plate must have had a dif- 
ferent shape from that of T. nigrita, being twice as wide as long (5 inches by 2 f inches) ; 
however, these measurements are taken from the osseous base without the horny 
covering, which probably would have been somewhat longer. The sternum is 24f inches 
long, and 23 inches broad between the lateral margins of the abdominal plates. It is 
deeply concave, and when the animal rested on the ground, it touched it with the sides 
of the sternum, which are thicker than the remainder of the carapace, and on a trans- 
verse terminal callosity produced by the reverted posterior margin of the sternum, which 
is straight, truncated, without excision. 
Another male example (specimen No. 3) agrees in every respect with the preceding, 
except in the sexual characters being much less developed, the specimen being only 
23 inches long, and therefore much younger. The first dorsal scute is more declivous 
towards the front, the concavity of the sternum less deep, and its terminal callosity 
only indicated by the very porous and rough surface of the bone. 
In our young example (18 inches long, specimen No. 4) the concentric strise are 
numerous, but not deeply cut ; and in this respect the present species is intermediate 
between T. nigrita and T. ephippium. The posterior end of the sternum is nearly 
truncate, the hind margin of each anal plate being obtusely rounded, and the plates 
being separated by so shallow a notch that, evidently, with advancing age, the sternum 
would have assumed the same truncate shape which we find in the adult specimens. 
It remains to add the principal measurements of the specimens examined: — 
Length of carapace. Width of carapace. Sternum. Caudal plate. 
In str. line. Over curv. In str. line. Over curv. Length. Width. Length. Width. 
Spec. no. inches. inches. inches. inches. inches. inches. inches, inches. 
1. e 31 37f 26. 40 24f 23 2ff 5 
2. $ 28f 361 23 35 22f 19 
3. 6 23 27^ 18 29 18f - 16f Iff 3f 
4. $1 ... 18 22 12i 19f 14 12 If 3 
5. $1 ... 15i 18i Hi 19 12i 11 If 2f 
~ Falconer, in his notes on Colossochelys atlas (Palasontolog. Mem. vol. i. p. 378), states that “ the thickness 
of hone in the convexity is almost in an inverse ratio to the size. The physiological reason of this is, that the 
smaller the animal, the more liable it is to injury, and it requires a greater arch to sustain it.” This view is 
not confirmed by an examination of the living Tortoises ; the Aldabra species is as large as those from the 
Galapagos, and even larger than one of these latter, yet it has a much thicker shell. We shall see that the 
extinct Mascarene species agree with the Galapagos Tortoises in this respect. Perhaps the cause of this is to 
be sought in the small quantity of earthy matter contained in the food on which those animals chiefly subsist, 
viz. succulent cacti. A living Galapagos Tortoise in my possession prefers, at present, the petals of a Westeria 
to every other plant. Of course, by the thinness of the shell its weight is much reduced, and these Tortoises 
are therefore able to walk faster and to carry the shell higher above the ground than the other species of this 
genus. The thinness of the shell and the slender osseous framework of the limbs are, in fact, characters correlated 
to each other. f Without epidermoid scutes. 
