20 CHELTDRrD.15. 



within the shell. Temporal region incompletely roofed over ; no 

 parieto-squamosal arch. Digits moderately elongate ; phalanges 

 w ith condyles ; claws four or five. 



The two closely allied genera which constitute this family agree 

 in tlie 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 

 comjjlcte ossification but late in life. Abdominal shields not meeting 

 on the median line, separated from the marginals by a series of 

 iuframarginals. Head large, incompletely retractile ; jaws strongly 

 hooked. Chin with one or more pairs of small dermal appendages. 

 Digits webbed. Fingers all clawed, outer toe elawless. Tail long, 

 crested above. Cervical vertebrce : second and third opisthocoelous, 

 fourth amphicyrtous, rest procoelous. 



1. CHELYDRA.. 



Chelydra, Sclmem. Prodr. p. 23 (1814) ; Fi'fzin'/. N. Class, lii-pt. 



p. 6 (1826); Wayler, Si/sf. Amph. p. 136 (1830); Grai/, Cat. 



Tort. p. 34 (1844), (mcl Sh. Eept. i. p. 48 (1855) ; Ayassiz, Contr. 



N. II. U. S. i. p. 416 (1857) ; Straueh, Chelon. Stud. p. 30 (1862) ; 



Grai/, Suppl. Cat. Sh. Rept. i. p. 64 (1870). 

 Chelonura, Fleminq, mil. Zool. ii. p. 270 (1822). 

 Rapara, Gray, Ann. PMl. (2) x. p. 211 (1825). 

 Saurochelvs, Latr. Fam. Nat. R. A. p. 92 (1825). 

 ChoWmwi, Rnfin. Atlant. Journ. p. 64 (1832). 

 Emysaurus, I)um. ^<f Bibr. ii. p. 548 (1835). 

 Chelonura, part., Ilolbrook, N. Am. Herp. i. p. 139 (1842). 



No supramarginal 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, pi. vi. (1792) ; Baud. Rept. 



ii. p. 98, pi. Ixxxvi. fig. 2 (1802); Leconte, Ann. Lye. N. Y. iii. 



p. 127 (18:30). 

 Chelydra lacertina, Schweigg, P)-odr. p. 23 (1814). 

 - — — serpentina, Schiveif/g. I. c. p. 24 ; War/l. Syst. Amph. p. 13(), 



pi. V. tigs. 46 & 47 (1830) ; Gray, Cat. tort. p. 34 (1844), tt7id Sh. 



Rept. i. p. 48, pis. xxxviii. fig. 1, ifc xl. fig. 2 (1855) ; Aqassiz, Contr. 



i. p. 417, pi. iv. figs. 13-1(5, & pi. v. figs. 18, 19 (1857); Peters, 



Man. Berl. Ac. 1862, p. 627 ; Straueh, Chelon. Stud. p. 139 (1862) ; 



Cope, Proc. Ac. Philad. 1872, p. 23. 

 Emys serpentina, Merr. Tent. p. 23 (1820). 

 Chelonura serpentina, Flemi/iy, Phil. Zool. ii. p. 270 (1822); Jlolbr. 



N. Am. Hcrp. i. p. 139, pi. xxiii. (1842) ; DeKay, N. York Faun., 



Rept. p. 8, pi. iii. fig. 6 (1842); Wied, N. Acta Ac. Leop.-Carol. 



xxxii. i. p. 47 (1865). 

 IJapara serpentina. Gray, Ann. Phil. (2) x. p. 211 (1825). 



