EMYS TECTA. 385 



amount of alar to marginal surface, there is tlie closest 

 agreement between the fossil and the recent forms. The 

 pectoral scutes in the recent form are rectangular and oblong 

 transversely, and the abdominal scutes nearly square ; the 

 anterior edge of each makes a sweep forwards as it rises 

 over the lateral keel, and then bends back to join on with the 

 corresponding marginal scute at an angle. In all these 

 there is a very close agreement between the plastron of the 

 fossil and of the recent form. 



The last point to be noticed concerns the interior of the 

 shell. In the Land Tortoises and the genera allied to Eniys 

 the hyposternal pieces of the plastron give off, on either side, 

 an apophysis which ascends on the inside of the third sterno- 

 costal piece as far as the first rib, and acts as a b^-ace or 

 buttress to strengthen the arch of the dorsal buckler. In 

 like manner the hyposternal pieces send off a similar apo- 

 physis on either side, which ascends along the inside of the 

 seventh sterno-costal piece up to the sixth rib, strengthen- 

 ing the carapace behind. In the small Emys tecta these 

 apophyses are greatly developed and expanded into wide 

 plates, like incomplete diaphragmata, which project into the 

 cavity of the shell, and contract the front and back apertures. 

 The anterior apophyses ascend nearly as high as the head of 

 the first rib, converging like the spandrels of a gothic arch. 

 These plate apophyses are constructed in the fossil on exactly 

 the same plan as in the recent species. 



In short, after a rigid comparison conducted through all 

 the details of size, form, relative proportion, and the dermal 

 characters, there is the closest agreement between the fossil 

 and the recent Emys tecta. The only discernible difference 

 is a sHght one of form, in the anterior vertebral scutes, 

 which are known to be very variable in different individuals of 

 the existing species, and the fossil does not appear to differ 

 more from these than individuals among them do from one 

 another. Hence arises the question, are we entitled to 

 regard the fossil Emys as belonging to the same species with 

 the Emys tecta"? The point is one of much importance, 

 both as it affects the established principles in Natural History 

 regarding the ideas comprehended under the name of species 

 and, in the present instance specially, from the fossils with 

 which the specimen was found associated. 

 . The received opinion in regard to the meaning of species 

 is, that all forms are to be considered of one and the same 

 species, which derive their origin from one and the same 

 kind of ancestors, or which do not differ more from these 

 than they do among themselves. Tried by this test, the 

 fossil as above described is clearly referable to the Emys 



VOL. I. c c 



