80 AMERICAN PERMIAN VERTEBRATES 



from the same horizon, and some at least from the same "bone- 

 quarry," has several maxillae and mandibles and other parts of the 

 skull of this same genus, and apparently this same species. 

 Strangely, however, as I have already stated, among the numerous 

 vertebrae accompanying them and the other genera I can find 

 none with long spines. Such vertebrae as have been restored 

 have rather short thin spines, resembling those of Varanosaurus, 

 etc., together with others which I refer to Nothodon. I give a 

 figure of a premaxilla from among these skulls. For the descrip- 

 tion of limb bones, some of which may belong with this genus, see 

 under Ophiacodon. 



Family Poliosauridae 



Case, Pelycosauria, 18, 1908. 



Primitive Pelycosauria with low, flat, acuminate head, sometimes elongate, 

 the maxillary with straight tooth line. One or more teeth at the anterior end 

 of the premaxillary and dentary, and one or more teeth in the maxillary 

 enlarged somewhat above the others. Maxillary teeth not separated from the 

 premaxillary teeth by a toothless interval. Vertebral spines low and the neural 

 arch free from the centrum through life in some (Poliosaurus). Abdominal 

 scutes present. Sacrum with two vertebrae. Long-bodied forms with long 

 tail; probably aquatic. 



The above definition by Case includes the most essential charac- 

 ters of this family, though the assumption that the animals were 

 probably aquatic is evidently wrong, and the separation of the 

 neural arches in Poliosaurus is not a family, nor even a generic, 

 character, since I doubt not it was due always to age. To these 

 characters may be added, as based chiefly upon the skeletons of 

 Varanosaurus described further on, the following: 



Twenty-seven presacral vertebrae (which number, however, 

 may be only of generic value); pubis elongated and expanded 

 anteriorly as in Dimctrodon; no clei thrum; the lower temporal 

 arch is incomplete below in some, perhaps all, the known genera. 

 To this family belong with assurance the following genera: Polio- 

 saurus, Ophiacodon, Theropleura, Varanosaurus, Poecilospondylus, 

 and other known yet undescribed forms. It is very doubtful 

 whether Elcabrosaurus belongs here, or indeed whether the name is 

 not a synonym. 



