1 ijO PLEURODIRA. 



Pi-CTnRAL Akch and FoiiE LiMii. — The rclomcdusidfe and 

 Clielydidir; are in this rcsj^ect very similar to the Testudinidse, 

 except that the humerus is less strongly curved, and the shape of 

 the coracoid varies within wider limits ; thus in Cheli/s the latter 

 1)0110 widens very considerably towards the cjncoracoid cartilage, 

 affecting a suhtriangular shape very similar so that of the same 

 bone in the Land-Tortoises ; in Podocnemis, on the contrary, tho 

 bone is very narrow and, apart from its being shorter in proportion, 

 resembles that of the Chclonida3 ; the other genera are intermediate 

 between the two extremes. The structure of the hand does not 

 differ consideraldy from that of the freshwater Testudinida- ; there 

 are nine carpal elements, but the radiale and centrale usually fuse, 

 and so do the two outer distal carpals in Emydura ; in the latter 

 genus and in Podocnemis there is a i)air of additional small bones, as 

 in many Euiyds. The phalanges number 2 . 3 . 3 . 3 . JJ, cxcejtt in 

 Pelomedusa, in which each finger has only two phalanges, the basal 

 and the second being fused into one. The genus Carettochdys, as 

 far as can be judged from the figure published, appears to have a 

 manus very similar to that of the Marine Turtles, the penultimate 

 plialanx of the second and third fingers being exceedingly elongate, 

 and the third finger is the longest ; only the two inner fingers are 

 provided with claws. 



Pelvis and Hind Limb. — All existing Pleurodira agree in having 

 the pelvis solidly united with the carapace and the plastron. The 

 ilium is expanded at its dorsal extremity, usually subtriangular in 

 horizontal Bcction, and, in the adult, bears no trace of sacral attach- 

 ment ; in the Pelomedusida) it is anchylosed to the last and penulti- 

 mate costal plates ; in Chelys, J/ydromedusa, and llhlnemys to the 

 pygal in addition to the two latter ; and in Chclodina, liydraspis, 

 Platemys, Emydura, and Elseya to the last costal and the pygal. The 

 pubis is anchylosed to the xiphiplastron on a comparatively^ small 

 surface, the extremity of the outer branch, the inner or symphysial 

 branch being perfectly free, slender, more or less dilated towards 

 the symphysis and directed forwards : it is nearly parallel with but 

 widely separated from the ischium. The latter bone is anchjlosed 

 to the xiphiplastron by its entire lower surface, which is directed 

 obliquely forwards and forms a symphysis with its fellow. With 

 the exception of Carettochdys, the hind limbs closely resemble those 

 of the freshwater Ciyptodira. The tarsus contains two bones in 

 the proximal row, a large inner (tibiale-(- intermedium) and a 

 small outer ; the centrale remains distinct in most genera, presenting 

 this peculiarity in CJidys that it extends to the inner border of tho 

 tarsus, separating the inner element of the distal row from that of the 

 proximal row ; the centrale fuses with the tibiale and intermedium 

 in C'helodina and Elseya, and with the tibiale, the intermedium, and 

 the fibulare in one specimen of Emydura mac(jtiarice. Kcckoniug 

 as tarsal the outer bono which is frequently termed the fifth meta- 

 tarsal, we have five tarsal bones in the distal row, and the phalanges 

 number 2.3.3.3.3, except in lUiinemys, which has only two 

 in the filth toe, and Pelomedusa, where, through fusion, they arc 

 reduced to 2. 2. 2. 3. 2 or 2. 2. 3. 3. 2. 



