74 THE AMERICAN NATURALIST. 
malian zygoma. This fact is further borne out by the very 
evident union of the two arches in Placodus and Cyamodus. 
If this is true, the Theriodonta (Cynodonta + Lycosauria 
+ Gomphodonta) cannot be the ancestors of the Squamata 
and Sauropterygia, as suggested by Cope (5). In these forms 
the history of the arches is very different. The Squamata 
possess only the superior temporal arch. | 
It is readily seen that the scheme here offered differs very 
little from that suggested by Baur in 1887 (6). The chief 
differences are the placing of the Pareiasauria as the most 
primitive group of the Reptilia, and the position of the masto- 
cephalous Reptilia in opposition to all the remaining Reptilia, 
the changes in the quadrate region being the determinate 
feature in both groups. The following Er will serve to 
make clear the ideas here expressed. 
Mammalia 
Theriodontia 
Dicynodontia, 
Sauromammalia 
Udenodontia Pelycosauria Rhyncocephalia 
(Mastocephalous group) (Saurocephalous group) 
eo 
ol 
SEELEY, H. G. On Pareiasaurus bombidens (Owen) and the Signifi- 
cance of its Affinities to Amphibians, Reptiles, and Mammals. 
Phil. Trans. Roy. Soc. Vol. clxxix, p. 97. 
SEELEY, H. G. Further Observations on Pareiasaurus. PAz/. Trans. 
Roy. Soc. Vol. clxxxiii, Pl. XVII, é. c. 1892. 
SEELEY, H. G. On the Anomodont Reptilia and their Allies. Loc. cit. 
Vol. clxxx, Pl. X, Figs. 4, 5, and 6. Q. 
4. BAUR AND CASE. On the Morphology of the Skull of the Pelycosauria 
and the Origin of the Mammals. Anat. Anz. Bad. xiii, Nr. 4 and 
5. 1897. 
5. Cope, E. D. Primary Factors of Organic Evolution. p. 115. 
6. Baur, G. On the Phylogenetic Arrangement of the Sauropsida. 
Journ. of Morph. Vol. 1, No.1. 1897 
coe 
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STATE NORMAL SCHOOL, MILWAUKEE, WIs. 
