PHYLOGENY OF SHELL OF TESTUDINATA 441 



ber of such bones scattered over its skull, but at its stage of life 

 these had doubtless become consolidated with the underlying 

 bones. 



It may be that the costal plates ought to be represented as 

 coming down to the peripherals. It appears to be assumed 

 that fontanelles in the carapace are the result of reduction of the 

 costal plates and peripherals and that this reduction, as well 

 as a flattening of the whole body, is due to an aquatic existence; 

 but we have lately learned that an African species of Testudo 

 has suffered a nearly complete loss of its shell and has at the 

 same time become excessively flattened (C. R. Acad. Paris, 

 vol. 170, 1920, p. 263). It appears not unreasonable to suppose 

 that in the most primitive turtles the costal plates had not yet 

 joined the peripherals; perhaps not yet the neurals. 



