TESTUDINID^:. 373 



America, taking a northwestern direction, they past into Asia over the bridge of land which 

 occupied the position of Bering Strait. Passing westward they entered Europe. Others 

 spreading southwestward peopled India and the strip of land which connected the latter 

 country with Africa, and which now, greatly deprest, is represented by Madagascar and 

 various groups of islands. From this land they entered Africa itself. 



The living Testudinidas which have been designated as "gigantic tortoises" all belong to 

 the genus Testudo. The species of Hadrianus of the Eocene were worthy of being called 

 gigantic. That the gigantic forms, living and extinct, may, in some cases, have been derived 

 from small species and that some of the smaller modern species are the descendants of extinct 

 gigantic ancestors, are possibilities. Within historical times gigantic tortoises have lived only 

 on islands, where there are no large carnivorous mammals. On the other hand, the large 

 Testudinidae of North America, from the Lower Eocene to the Pliocene, were exposed to the 

 attacks of large carmvora. 



As remarkt by Mr. R. Lydekker, the gigantic tortoises became extinct on all the conti- 

 nents at the close of the Pliocene. This appears to be true of North America, since the 3 species 



FIG. 471. Testudo sumeirei. View of living animal. After Rothschild's_figure, greatly reduced. 



recorded from the Equus beds are all of moderate size. Nevertheless, Dr. Leidy has figured 

 the claw phalange (Cont. Extinct Vert. Fauna West. Terrs., 1873, pi. xxxiii, fig. 21) of a species 

 of Testudo found in Pleistocene deposits in Hardin County, Texas. The individual must 

 have been one of great size. This phalange is now in the American Museum. We do not 

 know why some of the Pliocene gigantic tortoises should not have had descendants in the 

 Quaternary worthy of accompanying the great mammals of that period. 



Fig. 470 represents Testudo sumeirei Sauzier, a gigantic tortoise living in Port Louis, 

 Mauritius. This figure is reproduced from a plate publisht by the Hon. Walter Rothschild 

 (Novitates Zoologies, I, 1894, plate xi) over the name Testudo indica. This tortoise was men- 

 tioned in a treaty made in 1810. The length of the carapace is 40 inches (1015 mm.); that of 

 the plastron, 28 inches (711 mm.). 



ANALYSIS OF GENERA. 



A. Epiplastral lip projecting abruptly from front of carapace. 



a. Neural bones hexagonal. Eocene species Hadrianus 



aa. Usually some octagonal and quadrangular neurals; Oligocene to Recent species. . . Tatudo 

 A A. Epiplastral lip not projecting abruptly or far beyond gulo-humeral sulci. 



b. Epiplastral lip not thickened backward above; Bridger Achilemys 



lib. Epiplastral lip thickened backward above; Oligocene Stylemys 



Genus HADRIANUS Cope. 



Testudinidx with the plastron extensively united to the carapace by suture; with short 

 axillary and inguinal buttresses, the latter of which ascend within the sixth costal plates; no 

 plastral hinge. Epiplastral lip strongly developt; entoplastron wholly in front of the pectoral 



