8 CHELONIA. 



The arrangement of the bones or plates of the shell, as shown in 

 fig. 3, differs entirely from that of the overlying shields, both in 

 the upper shell (carapace) and lower (plastron) ; but the impres- 

 sions of the shields are nearly always distinct, as represented in 

 figures 8, 9, 10, 11, 12, 14. In these figures crosses are inserted 

 to indicate the position of the anterior (axillary) and posterior 

 (inguinal) processes or buttresses of the plastron, which, if present, 

 anchylose with the lower surface of the carapace. Figure 4 refers 

 to the terminology of the epidermal shields. 



Fig. 3. Shell of Morenia ocellata, showing bony plates. 



A. Carapace. B. Plastron. 



co. Costal. typp. Hypoplastron. nu. Nuchal. 



enp. Entoplastron. m. Marginal. py. Pygal. 



epp. Epiplastron. ne. Neural. xyp. Xiphip 



hyop. Hyoplastron. 



xyp. Xiphiplastron. 



The investigation of the bony plates presents no great difficulty, 

 and need not cause the slightest damage to the specimen, whether 

 dry or preserved in spirit ; for the removal of one or two epidermal 

 shields with a penknife requires but a little care, and after the 

 examination the horny shields may be stuck on again with gum 

 which is not soluble in alcohol. There is much greater variety, 

 apart from individual variations, in the disposition of the bony 

 plates than in that of the overlying shields, and much greater 

 profit is to be derived from the study of the former in determining 

 the relationship of genera of Tortoises. 



