THE DIVISIONS OF THE CHELONIA. 207 



geneva, the ilia unite by synchondrosis, or ankylosis, with 

 the last costal plate, and the pubis and ischium with the 

 xiphisternal plates, so that the pelvis becomes firmly fixed 

 between the carapace and plastron. 



The proximal row of the tarsal bones consists usually of 

 an astragalus, formed by the union of the tibiale and in- 

 termediuvi, and of a fibulare or calcaneum. In Chelydra 

 there is a centrale. In Chelone, Emys, Testudo, and 

 Trionyx, the centrale is united with the astragalus ; and in 

 Emys, the calcaneum coalesces into the astragalus, so 

 that the proximal portion of the tarsus consists of one 

 bone. In the distal series the two fibular tarsals are united 

 into a cuboid bone. There are five digits, and the fifth 

 metatarsal has a peculiar form, as if bent upon itself at 

 right angles, in the middle of its length. 



In the Testudinea there are only two phalanges in each 

 digit of the pes. 



The Chelonia are divisible into the Testudinea, the 

 Emydea, the Trionychoidea, and the Euereta. 



1. The Tes^itcimea have the horny jaws naked and cutting, 

 or denticulated. The eyes are lateral, the tympanic mem- 

 brane is exposed, the short and thick limbs have the toes 

 (all of which have nails) bound together by the integument. 

 The horny plates of the carapace and plastron are weU 

 developed. 



The Land Tortoises belong to this division. The cara- 

 pace is usually very convex, and sometimes (as in the genus 

 Pyxis) the anterior part of the plastron is moveable, and 

 can be shut up like a lid. In Cinyxis, the hinder part of 

 the carapace is similarly mobile. 



2. The Emydea have, usually, homy cutting jaws, un- 

 covered by lips ; the tympanum exposed, and the Kmbs more 

 slender than in the Testudinea, with five-clawed digits, 

 which are only united by a web. The horny plates of the 

 carapace and plastron are well developed. 



These are the River and Marsh Tortoises. They are further 

 divisible into two groups, in the one of which, the Terrapenes. 



