20 CHELYDRID®. 
within the shell. Temporal region incompletely roofed over; no 
parieto-squamosal arch. Digits moderately elongate; phalanges 
with condyles; claws four or five. 
The two closely allied genera which constitute this family agree 
in the following characters :— 
Carapace comparatively small, with serrated posterior border ; 
neural plates broader than long, forming a complete series; one or 
two pygals; twenty-three marginal plates. Plastron small, cruci- 
form, articulating with the carapace by gomphosis. The shell attains 
complete ossification but late in life. Abdominal shields not meeting 
on the median line, separated from the marginals by a series of 
inframarginals. Head large, incompletely retractile ; jaws strongly 
hooked. Chin with one or more pairs of small dermal appendages. 
Digits webbed. Fingers all clawed, outer toe clawless. Tail long, 
crested above. Cervical vertebrae: second and third opisthoccelous, 
fourth amphicyrtous, rest proccelous. 
1. CHELYDRA. 
spa est Schiweigg. Prodr. p. 23 (1814); Fitziny. N. Class. Rept. 
p- 6 (1826); Wagler, Syst Amph. p. 136 (1830); Gray, Cat. 
‘ort. p. 34 (1844), and Sh, Rept. i. p. 48 (1855) ; Agassiz, Contr. 
N. H, U.S.i. p. 416 (1857) ; Strauch, Chelon. Stud. p- 36 (1862) ; 
Gray, Suppl. Cat. Sh, Rept. i. p. 64 (1870). 
Chelonura, Fleming, Phil. Zool. i. p. 270 (1822). 
Rapara, Gray, Ann. Phil. (2) x. p. 211 (1825). 
Saurochelys, Lat. Fam. Nat. R. A. p. 92 (1825), 
Cheliurus, Rafin. Atlant. Journ. p. 64 (1832). 
Emysaurus, Dum. § Bobr. ii. p. 548 (1835). 
Chelonura, ‘part., Holbrook, N. Am. Herp. i. p. 189 (1842). 
Nosupramarginal shields. Orbit directed outwards and upwards. 
Tail with large shields inferiorly. 
North America to Ecuador. 
1. Chelydra serpentina. 
Testudo serpentina, Linn. S. N. i. p. 354 (1766) ; Schneid. Schildkr. 
p- 337 (1783); Schoepff, Test. p. 28, pl. vi. (1792) ; Daud. Rept. 
li. p. 98, pl. Ixxxvi. fig. 2 (1802); Leconte, Ann. Lye. N, Yai. 
p. 127 (1830). 
Chelydra lacertina, Schweigg. Prodr. p. 23 (1814). 
serpentina, Schweigg. l.c. p. 24; Wagl. Syst. Amph. p. 136, 
pl. v. figs. 46 & 47 (1830); Gray, Cat. Tort. p. 34 (1844), and Sh. 
Rept. i. p. 48, pls. xxxviil. fig. 1, & xl. fig. 2 (1855); Agassiz, Contr. 
i. p. 417, pl. iv. figs. 13-16, & pl. v. figs. 18, 19 (1857); Peters, 
Mon. Berl. Ac. 1862, p- 627 ; Strauch, Chelon. ‘Stud. p- 159 (1862) ; 
Cope, Proc. Ae. Philad. 1872, p. 23. 
Emys serpentina, Merr, Tent. p. 23 (1820). 
Chelonura serpentina, Fleming, Phil. Zool. ii. p. 270 (1822); Holbr. 
N. Am. Herp. i. p. ne pl. xxiii. (1842) ; oe Kay, N. York Faun. “ 
Rept. p. 8, pl. ii. fig. 6 (1842); Weed, 'N. Acta ‘Ac. Leop.-Carol. 
XXXll. i. p. 47 (1265). 
Rapara serpentina, Gray, Ann. Phil. (2) x. p. 211 (1825). 
