1864. | DR. J. E. GRAY ON THE CHELYDIDS. 129 
the Zoological Society’ for some additional observations on certain 
genera. 
The typical Chelydide form the first section. 
A. Head depressed, covered with a soft skin, which is sometimes 
more or less divided on the surface into numerous polygonal 
plates. The skull depressed, without any or only a very ru- 
dimentary zygomatic arch. Temporal depression large, with a 
more or less wide bony arch at the back, from the ear-bones to the 
middle of the occiput ; the temporal muscles only covered with 
a skin. Lower jaw weak, slender. The alveolar surface of 
the jaws thin, with a more or less distinct submarginal ridge. 
Typical CoeLyp1p#. 
a. The head very much depressed ; beak covered with flesh ; lips 
bearded. Skull very depressed, abnormal; temporal muscles 
very large, only covered with skin, without any central bony 
crown to the head; auri-occipital arch very slender, small ; 
lower jaw very slender, weak. CHELYDINA. 
1. Cuexys, Daud.; Gray, Cat. Shield Rept. 60. 
Matamata, Merrem. 
CueELys MATaMArtA, Gray, J. c. 60. 
Skeleton in Mus. Coll. Surg. no. 960, described by Owen, Cat. 
p- 187. Figured in Wagler’s N. S. Amph. t. 3. f. 5,15. Skull 
figured in Cuvier’s Oss. Foss. v. 2, t. 1]. f. 21-25, t. 12. f. 41. 
b. Head rather depressed, not fringed; beak naked; chin some- 
times bearded ; skull rather depressed, of normal form, with a 
distinct central bony crown, and a more or less strong auri- 
occipital arch; the auri-occipital arch very slender, weak; the 
temporal depression very large, covered with skin, separated by 
avery narrow ridge-like crown; shell very depressed, thin. 
Hypraspipina. (Fig. 1.) 
2. Hypraspis, Gray, J. c. 54. 
Intergular and nuchal plate on the margin. Chin two-bearded. 
Auri-occipital arch distinct. 
Hab. Tropical America. 
* Head very large, depressed, with small tessera. 
1. Hypraspis RANICEPS, Gray, /.c.55.t. 23. (Skull, figs. 1, 2.) 
Hab. Brazil. 
Skeleton in British Museum. 
Proc. Zoou. Soc.—1864, No. IX. 
