206 CHELYDID2&. 
7. Podocnemis tracaxa. 
Emys tracaxa, Spix, Test. Bras. p. 6, pl. v. (1824). 
macrocephala, SPU, la, DNs pl. ly. 
Peltocephalus tracaxa, Dum. &§ Bobr. ii. p. 378, pl. xviii. fig. 2 
(1835); Gray, Cat. Tort. p. 44 (1844), and Sh. fiepe. i. ps Gl 
(1855) : Strauch, Verth. Schildkr. p. 101 (1865); Gray, Suppl. 
Cat. Sh. Rept. i. p. 84 (1870). 
Carapace rather convex, obtusely keeled posteriorly. Supra- 
caudal shield sometimes single. Plastron large, front lobe much 
broader than the hind lobe, which exceeds the width of the bridge ; 
intergular shield longer than the gulars: the longest median suture 
is formed by the femorals; suture between the humerals about as 
long as that between the pectorals. Interorbital space flat, broader 
than the diameter of the orbit; upper jaw strongly hooked; jugal 
bone forming a suture with the quadrate; a very large interparietal 
shield, widening behind, and widely separating the parietals; the 
width of the mandible at the symphysis much exceeds the diameter 
of the orbit; alveolar surface of both jaws with a feeble median 
ridge. Chin with a short dermal appendage. ‘Three very large 
shields on the outer border of the foot. Dark brown above, 
yellowish inferiorly. 
Length of shell 43 centim. 
Amazon, Guianas. 
a, b, Ad., stffd. S. America. 
Fam. 9. CHELYDIDE. 
Emydide, part., Gray, Ann. Phil. (2) x. 1825 
Emydide, part., Bell, Zool. Journ. iii. 1828. 
Steganopodes, part., Wagler, Syst. Amph. 1830. 
Chelyde, part., Gray, Syn. Rept. 1831. 
Elodites Pleurodeéres, part., Duméril § Bibron, Erp. Gén. ii. 1835. 
Chelydide, part., Gr ay, Cat. Tort. 1844, and ‘Sh. Rept. 1. 1855. 
Chelyoide, Hydraspididee, part., Agassiz, Contr. N. H. U. 8. i. 1857. 
Chelyda, part., Strauch, Chelon. Stud. 1862. 
Hydraspididee, Cope, Proc. Ac. Philad. 1868, p. 282. 
Chelydidee, Hydraspidide, Gray, Suppl. Cat. Sh. Rept. i. 1870. 
Chelydide, Boulenger, Ann. §& Mag. N. H. (6) i. p. 347, 1888. 
Plastral bones nine. Shell covered with epidermal shields. Neck 
bending under the margin of the carapace, always exposed ; fifth 
and eighth cervical vertebra biconvex. No bony temporal arch, 
but usually a paricto-squamosal ; palatine bones separated by the 
vomer; nasals usually present; prefrontals separated from each 
other; dentary bones usually distinct. Digits moderately elongate ; 
claws four or five. 
South America, Australia, and New Guinea. 
