260 
DB. A. GrtjJNTHEE ON GIGANTIC LAND-TOETOISES. 
clearly and in exactly the same manner in the skulls. In the skulls of the broad form 
of carapace and sternum the palatal region is more concave than in the other ; the outer 
pterygoid edge is sharp in its entire length, or for the greater part of its length ; there 
is a deep recess at the base of the skull in front of the occipital condyle, and the 
anterior wall of the entrance into the tympanic cavity is considerably constricted. 
a. The first species (T. elephantopus ) is distinguished by a very short snout, and by 
an immensely developed and raised occipital crest (Plate 38. fig. A). 
j8. In the second ( T . nigrita) the facial portion is longer and the occipital crest low 
(Plate 88. fig. D). 
In the skulls of the narrow form, the palatal region is shallow, the outer pterygoid 
edge flattened in its whole length ; there is no deep recess at the base of the skull in 
front of the occipital condyle, and the anterior wall of the tympanic cavity is bulging- 
outwards, not constricted. 
y. In T. ephippium the tympanic cavity is much produced backwards, the tympanic 
opening elliptic, and the impression in front of the tympanic pedicle is very shallow 
(Plates 37 & 38. fig. C). 
b. The skull of a perfectly adult T. microphyes is only 83 millims. long, and has the 
characteristics of a young skull of one of its more gigantic congeners, neither the occi- 
pital crest nor the tympanic case being produced backwards. The impression in front 
of the tympanic pedicle is rather deep (Plates 37 and 38. fig. B). 
e. Finally, the skull of T. vicina has all the characteristics of that of T. ephippium , 
hut differs from it in having a circular tympanic opening. 
These observations fully bear out Porter’s and Darwin’s statements that the various 
islands are inhabited by distinct species. Unfortunately we do not possess positive and 
exact information as regards the localities whence our examples were obtained ; but 
Porter’s accounts are sufficiently detailed to enable us to relegate with more or less 
ce tainty some of the species before us to the places of their nativity. James Island 
yielded Tortoises of the broad, circular type ; and therefore either T. elephantopus or 
T. nigrita came from that island, probably the former. There can be no doubt that we 
have in T. ephippium the species inhabiting Charles Island ; and T. microphyes is most 
probably the representative from Hood’s Island. We may suppose that other specific 
forms exist ; but there is no evidence of them in the material before me. 
In young examples, which are rather common in collections, the distinctive characters, 
external or osteological, are incompletely developed, so that it is, at present, extremely 
difficult and somewat hazardous to refer very young individuals (up to about 15 inches 
in length) to the species to which they belong. This resemblance of young examples 
cannot be used as an argument against the distinctness of the various species, as gene- 
rally, in Vertebrates as well as Invertebrates, specific characters are not developed before 
a certain period, which varies exceedingly even in groups nearly related to one another. 
