1 1 12 CLASS REPTILIA. 



lated to the carapace, and has digitated lateral terminations, and 

 generally a larger or smaller median vacuity (fig. 1009). The 

 humerus is more or less flattened, with the axis of the head gen- 

 erally placed nearly immediately above that of the shaft, and the 

 radial process small, and placed more or less below the well- 

 developed head. The caudal vertebrae are proccelous, and the 

 cervicals extremely short. In the skull the temporal fossae are 

 completely roofed over by bone, so that the squamosal joins the 

 parietal ; and the bones of the palate unite for a longer or shorter 

 distance beneath the narial passage, so as to throw the posterior 

 nares more or less backward (fig. 1020). The prefrontals (as in 

 most Testudinidcz) always form a re-entering angle posteriorly ; and 

 the tympanic cavity is quite open posteriorly, so as to expose the 

 stapes. In old individuals the vacuities in the shell tend to ob- 



Fig. 1018. — Young of the Hawksbill Turtle (Clielone imbricata). Much reduced. 

 (After Bell.) 



literate, and in the more generalised extinct types this tendency is 

 much more marked, and it is quite probable that in some cases 

 they may have completely disappeared. This more complete ossifi- 

 cation of the shell in these generalised types indicates affinity with 

 the preceding families, and probably more especially with the 

 Acichelyidce ; and the same is indicated by other features, such as 

 the more marked constriction of the shaft of the humerus, and the 

 more oblique position of its head, together with the probable pres- 

 ence of claws to all the digits. Some writers, indeed, consider these 

 more generalised types as entitled to constitute a distinct family — 

 the P?'opleurid<z ; but their close relationship to the existing Log- 



