866 The American Naturalist. [October, 
centra generally notochordal ; 
generally present ; dentition abundant ; Pelycosauria. 
Ribs single-headed ; temporal fossa overroofed ; 
dentition abundant ; intercentra ; Cotylosauria. 
The Placodontia include the Placodontidae only. The Para- 
suchia include the Belodontidae, and probably the Aetosauridae. 
The Progansauria, the Mesosaurida;, the Procolophonidae, Palaeo- 
hatteriidae, Homoeosauridse, Proterosauridse and Rhynchosauridae. 
The Cotylosauria include the Pariasauridae and the Diadectidae. 
The Pelycosauria embraces the families of the Clepsydropidae, 
Pariotichidae, and Bolosauridae. The Anomodontia includes the 
single family of the Dicynodontidae, and perhaps the Endothio- 
dontidae. 
The Plesiosauria embraces the following families : Plesiosau- 
ridae, Nothosauridae, and Lariosauridae. 
The Squamata is an extended group, which is represented by 
three sub-orders, which are defined as follows : 
Alisphenoid modified as epipterygoid, or wanting, 
leaviqg brain-case open ; parietals flat ; an 
interclavicle and clavicle ; teeth with dentinal 
roots ; Lacertilia. 
Epipterygoid present; parietals decurved, par- 
tially enclosing brain-case ; no clavicle nor 
interclavicle ; teeth with osseous roots ; Pythonomorpha. 
No epipterygoid ; brain-case enclosed in front ; no clavi- 
cle nor interclavicle ; no fore-limbs; Ophidia. 
The Lacertilia embraces the following superfamilies. 
I. Prootic not produced beyond arched body; acrodont ; 
olfactory lobes not underarched ; two suspensoria. 
No clavicTe"lior interclavicle ; no columella ; 
tongue papillose, extremity sheathed ; Rhiptoglossa. 
A clavicle proximally simple; an anchor- 
shaped interclavicle ; a columella ; tongue 
papillose, not sheathed ; Acrodonta. 
II. Pro6tic bone not produced beyond arched body ; den- 
tition pleurodont; olfactory lobes not underarched; 
two suspensoria. 
