144 AMERICAN PERMIAN VERTEBRATES 



rugosus Case, dorsal vertebra, two-thirds natural size; Fig. 2, Nothodon lentus 

 Marsh, dorsal vertebra; Fig. 3, Ophiacodon, posterior dorsal vertebra; Fig. 

 4, Ophiacodon (?), Sphenacodon (?), last lumbar and first sacral vertebra, 

 from in front; Fig. 5, Ophiacodon minis, part of left maxilla, type specimen. 



Plate XXXVII. — New Mexico, Yale collections. Fig. 1, Sphenacodon 

 minis, Marsh, left maxilla, from within (part of type specimen); Fig. 2, 

 Sphenacodon ferox, left premaxilla, from without; Fig. 3, Ophiacodon (?), 

 Sphenacodon (?), left femur, dorsal side; Fig. 4, Ophiacodon, left ilium, from 

 without; Fig. 5, the same, from within; Fig. 6, Plalyhystrix rugosus Case, 

 spine of posterior vertebra. 



Plate XXXVIII. — New Mexico, Yale collections. Aspidosaurus novamex- 

 icanus Williston, type specimen, from above, about one-half natural size; 

 Fig. 2, Limnoscelis paludis Williston, a little reduced; Fig. 3, Nothodon lentus 

 Marsh, top of skull, reduced. 



