
536 The American Naturalist. [June, 
cervicals with double articular faces; sacral ribs well developed, 
and connected with centrum and neuroids. Pelvis free from 
plastron and carapace. Epiplastra in contact with hyoplastra, 
entoplastron oval, rhomboidal or T-shaped; a more or less com- 
plete series of peripheralia more or less connected with the ribs. 
IV. Chilote (Trionychia). 
No free nasals; no parieto-squamosal arch; descending processes 
of prefrontals connected with vomer or not ; stapes entirely sur- 
rounded by quadrate; pterygoids broad, without wing-like lateral 
expansions, separating quadrate and basisphenoid ; epipterygoid 
free ; dentary bones united. Cervical vertebre with very rudimen- 
tary transverse processes in front of vertebra; the posterior cervicals 
with double articular faces; sacral ribs well developed, and con- 
nected with neuroids only. Pelvis free from plastron and cara- 
pace; epiplastra separated from hyoplastra by the v- shaped 
entoplastron; marginal bones absent, or forming an incomplete 
Series, not connected with the ribs. 
