GIG-ANTIC TORTOISE FROM MADAGASCAR. 307 



of the carapace and plastron in the tortoise now described leads to T. hololissa, which 

 differs from T. elephantina in the smaller plastron not notched behind ; from T. gigantea 

 in the undivided supracaudal shield ; and from T. daudini in the wider plastral bridge. 

 T. grandidieri may be distinguished from T. elephantina, hololissa, and gigantea by the 

 greater depression of the carapace. 



2. Skull. — The remains on which Testudo grandidieri was established did not include 

 any portion of the skull. It is therefore highly gratifying to find among the bones 

 secured by Mr. Last a nearly complete skull, 15 centim. long (to the extremity of the 

 supraoccipital crest), wanting merely the zygomatic arch and the right quadrate. This 

 skull was associated with the female shell noticed above. The mandible of this 

 specimen is also present, together with a symphysial fragment of another. 



The structure of the skull fully confirms the conclusion arrived at by Prof. Vaillant, 

 from the study of the shell, as to the close affinity of T. grandidieri to the Aldabra 

 Tortoises. The differences, in fact, are rather slight and, in some respects, show an 

 exaggeration of the features which differentiate the Aldabra forms from their congeners. 



The naso-frontal region is moderately convex, with the nasal fossa extremely large 

 and produced to between the anterior portion of the orbits, sloping obliquely down- 

 wards, and longer than broad. When the skull is viewed from above, the anterior 

 portions of the choanse, separated by a naiTow septum, are visible through the nasal 

 fossa, whilst the prsemaxillaries terminate on a line with the anterior borders of the 

 orbits. The interorbital region is formed entirely by the praefrontal bones, the upper 

 surface of which is much more developed than that of the frontals. The postorbital 

 arch is slender and the parietal bones narrow. The prsefrontals form a broad suture 

 with the postfrontals, and the frontals are enclosed between these two elements and the 

 parietals. The prsefrontals are longer than broad, and their median suture measures 

 two-fifths that between the frontals ; the latter are very slightly longer than broad, and 

 measure half the greatest length of the parietals. The diameter of the tympanic cavity 

 equals that of the orbit. 



The lower aspect of the skull presents this peculiarity, that the pterygoids do not 

 meet on the middle line, being separated by the basisphenoid, as I have recently 

 described in T. microtympanum^. The vomer is produced posteriorly far beyond 

 the line of the postorbital arch, and its length equals nearly four times that of the 

 choanse ; it bears a feeble median keel, which is continued on the anterior half of 

 the basisphenoid ; the palatines extend but little beyond the vomer. The suture 

 between the prsemaxillaries and the vomer falls a considerable distance behind the 

 inner angle of the alveolar edges of the maxillaries. The alveolar surface of the 

 maxillary is broad, with a strong denticulate median ridge, which is equally distant 

 from the likewise denticulate inner and outer margins. The occipital condyle is 

 tripartite, and the posterior margin of the opisthotic is not excised. 



' Proc. Zool. Soc. 1891, p. 5, figs. 1, 2, 3. 



2t2 



