674 The American Naturalist. [July, 
gastroid well-developed, separating completely entopubes and entois- 
chia; number of peripherals 11; an entoplastron. Number of neuralia 
complete; posterior pleurals meeting in median line. Chelydra, 
Macrochelys. 
3. Staurotypidæ. 
Frontals excluded from orbit; maxillary in connection with quad- 
ratojugal; squamosal without connection with postfronto-orbital ; 
mesogastroid well-developed; separating completely entopubes and 
entoischia; number of peripherals 10; an entoplastron ; number of 
neuralia incomplete; | potete pleurals meeting on median line. 
Staurotypus, Claudi ; 
4. Kinosternide. 
Frontals excluded from orbit; maxillary in connection with quad- 
ratojugal ; squamosal without connection with postfronto-orbital ; meso- 
gastroid reduced ; number of peripherals 10; no entoplastron; num- 
ber of neuralia incomplete; posterior pleurals meeting on median 
line. Kinosternon, Aromochelys, Goniochelys. 
III.—PLATYSTERNOIDEA. 
No parieto-squamosal arch; a foramen palatinum between palate 
and maxillary; articular faces between sixth and seventh cervical not 
plane; nuchal without lower and without a lateral pr 
biconvex cervicals; a complete series of inframarginals, Skull of 
the type of the Chelydroideae. 
Platysternide. 
Frontals excluded from orbit; maxillary in connection with quad- 
ratojugal ; jugal excluded from orbit; squamosal connected with post- 
fronto-orbital ; mesogastroid well-developed, separating completely ento- 
pubes and entoischia; number of peripherals 11; an entoplastron ; 
number of neuralia complete. Platysternum. 
1 In Claudius the puro one aids is exceedingly slender; the parietal sends down 
a process behind the p ital to join the jugal. The zygomatic arch is also 
very slender, but three times asbroad as the postorbital; the interorbital arch is one 
and a half times the diameter of the orbit. The lower jaw is strongly hooked, with 
the symphysis larger than the diameter of orbit. Upper jaw with a small but distinct 
hook, each maxillary with a very sharp lateral hook. Lower side of skull as in 
Kinosternon ; palate not forming a part of the alveolar surface, the posterior nares not 
bridged over by palate and vomer as in Staurotypus. Pterygoids without any eéto- 
pterygoid process. 
