SYSTEMATIC REVISION OF THE SUBORDER. 7 1 



ently no supratemporal foramen, but a large infratemporal, whicli extends well upwards. 

 There is no parieto-quadrate arch. An element, perhaps supraoccipital, terminates 

 in a free appressed apex on each side of the median posterior region. This may be 

 homologous with the small free bone described in Naosaiiriis in nearly the same 

 position. The stapes is very large, and is at least partially perforated near the 

 expanded proximal extremity. It is probably fully perforated as I have described it 

 in the Diopeus leptocephaliis." 



Edaphosaurus mlcrodus Cope. 



Proc. Am. Phil. Soc, vol. xxii, 18S4, p. 37. Also Pal. Bull. 39. 



This is a synonym of Naosaurus microdus Cope, which see. 



Table I. — Showing the Characters of the Suborder Pelycosauria. 

 Characters common lo the primitive reptiles. 



1. Vertebrae notochordal. 



2. Intercentra present. 



3. Interclavicle, clavicle and cleithrum present. 



4. Entepicondylar foramen present. 



5. Pelvis narrow. 



6. Five elements in the distal row of the tarsus. 



Characters common to the Diapsida. 



1. Two lateral temporal fenestra?. 



2. Squamosal and prosquamosal separate, not closely united with the quadrate. 



3. Opisthotic closely united with the exoccipital, but the suture distinct in some specimens. 



4. Prevomers large and the vomers reduced. 



5. Cranium short and the facial region elongate. 



6. Axis with large free intercentra and neural arches. 



7. Phalangeal formulae, probably, 2, 3, 4, 5, 3, in the pes and 2, 3, 4, 5, 4, in the manus. 



Characters distinctive of the Pelycosauria. 



1. Typical forms terrestrial. 



2. Skull becoming laterally compressed and elevated in the facial region. 



3. Anterior teeth, incisors and canines, becoming elongate and tusk-like, with sharp cutting edges, sometimes 



even crenate. 



4. Development of a toothless diastema. 



5. External process of the pterygoid becoming very heavy and prominent. 



6. Carpus and tarsus reaching a high stage of development. The individual bones well formed and closely 



interlocking without a great deal of cartilage. 



7. The bones of the pelvis united into a strong basin. 



8. Tail becoming short and the spines becoming enormously elongated in the most specialized forms. 



Table II. — Contrasting the Families of the Pelycosauria. 



I. PoliosauridcE. 



1. Skull low and acuminate (Proterosaurian). 



2. Tooth line of the maxillary straight or nearly so. Diastemal notch absent or poorly developed. 



3. Neural spines short. 



4. Sacrum with two vertebrae. 



II. ClefsydropidcE. 



1. Skull laterally compressed and the facial region elevated. 



2. Tooth line of skull convex. Diastemal notch present. 



3. Neural spines very high. 



4. Sacrum with three vertebrae. 



