206 DR. J. E. GRAY ON THE TORTOISES. [ Mar. 11, 
the alveolar surface broad, expanded, nearly as broad behind as in 
front, the centre of the outer edge produced and acute, with a large 
concavity on each side behind it, and with an irregular sharp-edged 
ridge nearer the inner edge than the outer margin, with a conical 
compressed prominence in front; the labial margin with a series of 
conical teeth. 
Pag, 15: 
Pseudemys serrata. 
A second skull depressed, ovate, sides of the face shelving ; nasal 
aperture very large; orbits very large, superior, separated by a very 
narrow space; crown rhombic, produced behind; zygomatic arch 
very broad, convex, nearly as wide as the back edge of the orbit and 
the front edge of the oval tympanic cavity. Upper jaw with a well- 
marked irregularly dentated ridge parallel with the outer edge, and 
a broad flat space behind it; there is a conical tooth on the front 
end of the ridge, and a deep conical pit on the front of the upper 
jaw. Hinder nasal opening arched in front, near the middle of the 
palate. The lower jaw strong, broad, expanded ; lower surface flat ; 
upper surface with a short denticulated marginal edge, and a conical 
central prominence in front, with a central longitudinal ridge and a 
stronger arched ridge parallel with the outer margin. Toes long, 
slender, broadly webbed. 
2. PsEUDEMYS DECUSSATA. 
Pseudemys decussata, Gray, Ann. & Mag. N. H. xii. p. 183. 
