FOSSIL VERTEBRATES — REPTILIA 521 
Order Paretasauria. 
Fam. Paretasauridae (African forms). 
Diadectidae (American forms). 
Pariotichidae (American forms). 
Elginidae (European forms). 
Order Anomodontia. 
Suborder Dicynodontia. 
Placodontia. 
Theriodontia. 
The Dicynodontia, including the genera Dicynodon, Oudenodon, 
and Piychosiagum (Ptychognathus), are all from the same locality, 
South Africa, as Pareitasaurus, and from the same geological 
horizon. 
Dicynodon is known only from the skull and is one of the 
most peculiar of the reptilian forms ; the jaws were edentulous 
except for the presence of two large tusk-like teeth that grew 
out from the anterior part of the upper jaw just in the position 
occupied by the canine teeth in the mammals; the part of the 
upper jaw anterior to these teeth and the lower jaw were pro- 
tected by a horny sheet similar to that present in the turtles ; 
the posterior part of the skull was perforated by large fossae 
that served to lighten it considerably. This process of lightening 
the skull by the development of large fossae in the posterior, 
temporal portion, is a constant feature of all the reptiles above 
the Parciasauria with the exception of the turtles. Many scat- 
tered bones have been found in the same deposits as the skulls 
of Dicynodon that may belong to the same genus, but there is 
not sufficient evidence to say definitely that this is true, and 
until the vertebral column and the limb bones are made out it 
« Elginia is an imperfectly known form from the Elgin (Triassic) sandstones of 
Scotland. There are no bones preserved, but only the impression of the bones in the 
soft sandstone from which all the bony tissue has rotted out. The fossils were studied 
from casts made of the cavities left by the decayed bones. The animal was of con- 
siderable size, nearly as large as Parezasaurus and the teeth were arranged in a regu- 
lar series around the edges of the jaws; the appearance of the skull in life must have 
been most peculiar, the presence of strong rugosities on the surface of the bones of 
the skull show that the head was covered with large horns. Gez&¢a was a related form 
from the same locality and horizon. 
