206 CHELONIA. 



Pleurosternum bullocki (Owen 1 ). 



Syn. Platemys bullocki, Owen 2 . 



Meyasternum koeniyi, Gray 3 . 

 Pleurosternum concinnum, Owen 4 . 

 Pleurosternum ovatum, Owen 5 . 

 Pleurosternum emaryinatum, Owen G (in }) arte). 

 Platemys concinna, Maack 7 . 

 Platemys ovata, Maack 8 . 

 Diyerrhum bullocki, Cope 9 . 



The type species. Of large size ; the carapace of adult individuals 

 attaining a length of about 0,480 (19 inches). Eutoplastral usually 

 much wider than long, and intergular shield of a regular shield- 

 shape. 



The whole of the specimens described under the above-mentioned 

 name are, at least provisionally, included under a single species, 

 since there are no valid characters by which they can be distin- 

 guished. 



In the young the first pair of marginals encroach to such a large 

 extent on to the anterior border of the nuchal as to leave only a 

 very small portion free. This condition may perhaps have 

 persisted in the type carapace of P. concinnum 10 . The bridge was 

 also relatively shorter in the young than in the adult. In 

 extremely young individuals the vertebral shields of the carapace 

 appear to have been divided mesially. Although there is a certain 

 amount of variation in the relative width of the plastron of different 

 specimens, yet there is such a gradual transition from one to another 

 that it appears impossible to found satisfactory specific differences 

 on such characters, and the whole of the specimens are therefore 

 provisionally included under one name. In the figure of the type 

 plastron of P. concinnum the two diameters of the eutoplastral are 

 represented as nearly equal ; but it appears from the text that the 

 transverse is in reality the longer of the two. 



1 Eep. Brit. Assoc, for 1841, p. 164 (1842).— Platemys. - Log. eit. 



3 Oat. Tortoises &c. Brit. Mus. p. 45 (1844). 



4 Wealden and Purbeck Eeptilia (Mon. Pal. Soc), pt. i. p. 3 (1853). 



5 Ibid. p. 8. G Ibid. pis. v., vi. 



7 Palaiontographica, vol. xviii. p. 288 (1869). 8 Ibid. p. 203. 



9 Trans. Arner. Phil. Soc. vol. xiv. pt. i. p. L56 (1870). 



10 Owen's ' Wealden and Purbeck Eeptilia,' pi. ii. It might be urged that this 

 should be considered as a specific distinction. Since, however, this feature 

 occurs in all young individuals and is unknown in any other adult carapace, 

 it can only be regarded as an abnormality, even if the figures be correct, and 

 there is some confusion therein between sutures and sulci. 



