CHELYDRIDZ. 19 
The following figure refers to the terminology of the epidermal 
shields of the shell. 
Fig. 2. 
Chelone mydas. 
A. Carapace. B. Plastron. 
a, Abdominal. h, Humeral, n. Nuchal. 
an, Anal. ig. Intergular. p. Pectoral. 
e. Costal. tm. Inframarginal. se, Supracaudal., 
f. Femoral. m. Marginal. v. Vertebral. 
g. Gular. 
Fam. 2. CHELYDRIDZ. 
Emydide, part., Gray, Ann. Phil. (2) x. 1825. 
Emydide, part., Bell, Zool. Journ, ili. 1828. 
Steganopodes, part., Wagler, Syst. Amph. 1850. 
Emyde, part., Gray, Syn. Rept. 1831. 
Elodites Gieradane, part., Duméril & Bibron, Erp. Gén. ii. 1835. 
Emydide, part., Gray, Cat. Tort. 1844, and Sh. Rept. i, 1855, 
Chelydroide, Agassiz, Contr. N. H. U.S. i. 1857, 
Chersemyda, part., Strauch, Chelon. Stud. 1862. 
Chelydride, part., Gray, Suppl. Cat. Sh. Rept. i. 1870. 
Chelydrine, part., Cope, Proc. Ac. Philad. 1872, p. 22. 
Chelydride, part., Cope, Proc. Am. Philos, Soc, xx. 1882, p. 144, 
Nuchal plate with long costiform processes, underlying the mar- 
ginals. Plastral bones nine. Shell covered with epidermal shields. 
Caudal vertebre mostly opisthoceelous. Neck completely retractile 
4 D 
