116 Dr. C. W. Andrews on some 



nearly complete carapace and plastron of a tortoise from the 

 Upper Eocene beds from ^vllich PaJceomosiodon and Arsinoi- 

 therium have been obtained. This specimen was found in 

 slightly compacted sand, close to one of the numerous groups of 

 logs of silicitied wood which form such a characteristic feature 

 on the surface of beds of tliis age in the region in question. 

 The shell was lying somewhat on its side, so tliat the left- 

 hand edge was exposed and had been partly removed by the 

 sand-drift, but the rest, comprisiiig considerably more than 

 three fourths cf the shell, was preserved, and the pelvic bones 

 were in position. Both carapace and plastron, however, were 

 cracked in every direction, so that it was very difficult to 

 remove the specimen without further injury ; at the same 

 time the sliell is quite undistorted by pressure and gives an 

 accurate idea of the form of the living animal. 



In its general shape this Chelonian resembles Podocnemis 

 wadagascariensis, but is rather more convex, particularly in 

 the region covered by the last vertebral shield, where there is 

 a well-marked prominence. The carapace is slightly expanded 

 posteriorly. 



The Carapace (PI. YII. fig. A). — There are seven neural 

 bones, the series being separated from the nnclial in front and 

 the suprapygal behind by the union in the middle line of the 

 anterior and posterior pairs of costals respectively. The dis- 

 tance between the anterior neural and the nuchal is 4(3 raillim., 

 that between the posterior neural and the suprapygal 19 millim. 

 The anterior neurals are much longer than wide, but they 

 shorten from before backward, so that the posterior ones are 

 wider than long. They are hexagonal in outline (except the 

 first and last, which are pentagonal owing to the suppression 

 of the anterior and posterior faces respectively), and in the 

 anterior ones the antero-lateral border is much shorter than the 

 postero-lateral. 



There are eight pairs of costals ; as already mentioned, 

 the anterior and posterior pairs meet in tiie middle line. The 

 nuchal {Nu.) is large and is wider than long; its anterior border 

 is emarginate. There are eleven pairs of marginals, of which 

 4, 5, 6, and 7 form the base of the bridge, and 5 and 6 unite 

 with the mesoplastral {Ms. p.). The anterior buttress is opposite 

 the lourth marginal, the posterior one opposite tlie seventh. 

 The anterior marginals have a rounded edge ; the posterior are 

 somewhat expanded and have a sharp edge. The pygal is 

 notched in tJ>e middle line by the furrow separating the 

 posterior pair of marginal shields. The suprapygal [Pyg.) 

 occupies the summit of the posterior prominence above referred 



