Chelonia. 



39 



Here are placed the fossil remains of the order CHELONIA, Wall-cases, 



most largely represented at the present day, including the Nos *m 1 lt J 12> 



Tortoises and Turtles, a group of reptiles in which the verte- ca^s & 



brse and ribs are immovable, being combined with the external Nos. 19, 20-' 



coat of bony plates, closely connected by interlocking sutures, 21 



FIG. 48. Outline of the Carapace, or dorsal 

 shield, of Hardella Thuryi (Gray), reduced. 

 nu, nuchal ; nl-n8, neurals ; cl-c8, costals ; spy, 

 1 <fc 2, suprapygals; py, pygals ; ml-mll, mar- 

 ginals. In both these figures the outlines of the 

 bones have wavy sutures, the firm dark lines show 

 the outlines of the overlying horny shields. 



FIG. 49. The plastron, or ventral shield, of 

 Cachuga tectum (Gray), reduced ; ep., epiplastral 

 bone; entp., entoplastral bone ; hy.p., hyoplaetral 

 bone ; xp., xiphiplastral bone ; g, gular shield ; 

 hum., humeral; pec., pectoral; ab., abdominal; 

 fern., femoral ; and an., anal shields. 



The originals of Figs. 48 and 49 are both from the Pliocene, Siwalik Hills, India. 



enclosing the entire body of the animal. This box-like 

 envelope is covered with leathery skin or horny shields ; one 

 kind of which is called "tortoise-shell," and is made into 

 combs, &c. There are no teeth, the jaws being encased in a 

 horny beak, the sharp edges of which serve instead for 

 dividing the food. 



The Chelonians are found living at the present day on land, 

 in fresh water, and in the sea; they are all oviparous, depositing 

 their eggs in the sand, to be hatched by the warmth of the sun. 

 Some recent Turtles' eggs from Ascension, cemented together 

 and fossilized in shell-sand by deposition of lime (produced 

 through the rapid evaporation of the sea-water by the sun's 

 heat), are exhibited in Wall-case, No. 12. 



Wall-case 

 No. 12. 



