30 DERMATEMYDID&. 
lobe movable ; with four pairs of shields, of which the posterior or 
anal are usually coalesced into a single shield; a very small gular 
may be present; abdominals separated from the marginals by two 
shields. Beak scarcely hooked; jaws with a single sharp edge; 
orbits directed upwards; postorbital and temporal arches moderate. 
Chin with a pair of barbels. Digits webbed. Tail short. 
Central America. 
Fig. 9. 
Skull of Stawrotypus salvinii. (From Gray, P. Z. 8. 1869.) 
The two species agree in the following characters :—Vertebral 
shields not broader than long, not two thirds the width of the 
costals; an emargination in the posterior border of each of the 
vertebral and costal shields, corresponding to the three keels which 
run along the carapace. Head extremely large; a large horny 
shield covers the upper jaw, another the mandible, and a third the 
upper surface of the snout; soft parts with small warts; tympanum 
indistinct under the thick skin. Wrist and heel with curved band- 
like lamelle. Male with a patch of small horny, sharp-edged 
tubercles on the lower surface of the leg and another under the 
thigh. Tail with more or less distinct small conical tubercles, 
forming paired longitudinal series. 
In 8. salvinit the neural plates are seven in number, about as 
broad as long; the last is separated from the pygal by the seventh 
pair of costals; the eighth pair of costals is separated by the pygal, 
which is either single or divided into a small anterior and a large 
posterior plate. The hyoplastral bones have a greater share in the 
formation of the bridge than the hypoplastrals. 
