864 The American Naturalist. [October, 
The quadrate bone in contact only with adjacent 
elements; no intercalare; supratemporal pies- 
ent ; ribs one-headed ; Squamata 
The order Ichthyopterygia embraces the families of Ichthyo- 
sauridae and Mixosauridae. 
Two families enter the Ornithosauria, viz., the Pteranodonti- 
dae and the Pterodactylidae. 
The DiNOSAURiA embraces two suborders, as follows: 
Inferior pelvic elements directed downwards ; Saurischia. 
Pelvic elements directed backwards ; Orthopoda. 
The families of the Saurischia are the Cetiosauridae, Coeluridae 
and Megalosauridae. Those of the Orthopoda are the Agathaum- 
idae, Omosauridae, Scelidosauridae, and Iguanodontidae. 
The order Crocodilia embraces one suborder, as follows : 
Nareal canal underoofed to behind larynx ; no epip- 
terygoid, nor clavicle ; pelvis excluded from 
acetabulum ; Eusuchia. 
Under the Eusuchia we know the families Crocodilidae, Gonio- 
pholidae, and Teleosauridae. 
The Rhynchocephalia is a varied order. Its contents fall 
into two suborders : 
Premaxillary region forming a toothless beak ; ribs 
with uncinate process ; Sphenodontina. 
Premaxillary region not beaked ; uncinate processes 
wanting ; Choristodera. 
To the Sphenodontina belongs the Sphenodontidae. The 
Champsosauridae from the suborder Choristodera, on account of 
their many peculiarities, the most important of which now known 
is the separation of the as dentatum from the axis. 
The order Testudinata presents four subordinal modifica- 
tions, as follows : 
I. No descending processes of the parietal bones. 
Vertebrae and ribs free and separated from a bony 
exoskeleton ; no descending processes of the 
parietals ; Atheccs. 
II. A carapace and plastron, and descending process of 
parietals. 
