STUDIES FOR STUDENTS. 
20508, IDe aOR MUTIN I AINID) CiHOLOCEICAIG IRIAILAINIOINS 
UF Tse, VIS)RIOS IS IRVAIUE,S,. 
Ill. REPTILIA. — (Continued.) 
THERIODONTA.—This name is applied to what must be con- 
sidered as a very unstable order of the reptilia. Composed as it 
is of the least well understood of the reptilian forms, it may at 
any time fall asunder under the light of new discoveries and be 
seen to be composed of several well defined orders instead of 
being a single one. The animals making up the order were 
originally placed by Owen in his Anomodontia, in the family Cyno- 
dontia, but were soon taken out and placed in a separate order, 
the Zheriodonta. Owen’s classification was arranged on the 
forms from South Africa only, and it was soon found that it 
would not suit the forms from America and Russia. Many 
schemes have been proposed to accommodate all of the different 
groups, but none has been arranged as yet that is at all satisfac- 
tory; there seems to bea general recognition of three distinct 
groups, but the value of these is a matter of much dispute. 
Lydekker, in his catalogue of the reptiles of the British Museum, 
would call the 7heriodonta a suborder of the order Anomodontia, 
while Seeley, of the same institution and on the evidence of the 
same material, raises many forms that Lydekker regarded as 
families into separate and distinct orders. A quite common 
opinion among paleontologists, and one that may be of the 
greatest service to the student, is to regard the 7heriodonta as an 
order and the three separate groups as suborders — the Pelyco- 
sauria, the Cynodontia, and the Gomphodontia. ; 
The first of these the Pelycosauria, is represented most largely 
in the Permian deposits of the United States, but a few isolated 
622 
