SYSTEMATIC REVISION OF THE SUBORDER. 



Order RHYNCHOCEPHALIA. 

 Suborder PELYCOSAURIA Cope. 



Proc. Am. Phil. Soc, vol. xvii, 1878, p. 511. Also Pal. Bull. 29. 



Original description : The Pelycosaiiria was first regarded by Cope as belonging 

 to the order Rhynchocephalia in a description of Clepsydrops natalis. "Of the general 

 affinities of this genns {Clepsydrops) it is only necessary now to state that my ref- 

 erence of it to the Rhynchocephalia is confirmed. It differs from the recent species 

 of the order in the absence of the quadrato-jugal arch and the remarkably developed 

 ischia. On this account I refer to Clepsydrops and its allies as a distinct suborder 

 under the name Pelycosauria.^'' 



For the description of the ischium see the original description of the 

 genus Clepsydrops, p. 37. The first of the characters mentioned in the 

 original description has been proved to be erroneous, but the second, with 

 characters of later discovery, shows that the Pelycosaiiria is unquestion- 

 ably entitled to subordinal rank or, if Osborn's classification be prefeiTed, to 

 ordinal rank in the subclass Diaplosauria* 



Revised description : Primitive Diapsidan reptiles, mostly adapted to land life, 

 but with some littoral and swimming forms. Carnivorous and predator>'. Skull low 

 and flattened to high and thin. Teeth simple with strong crenate cutting edges in 

 the most specialized forms. Incisors and anterior maxillary teeth becoming enlarged. 

 Vertebra; notochordal. Intercentra present. Ribs two-headed. Neural spines much 

 elevated in the most specialized forms. Interclavicle T-shaped. Coracoid and pre- 

 coracoid separate from scapula until late in life. A rudimentary cleithrum present. 

 Humerus with entepicondylar foramen. Pelvis narrow and high ; the bones closely 

 united ; the two sides of the pelvis meeting in a deep median symphysis. Tarsus 

 with five elements in the distal row. Phalangeal formula probably that characteristic 

 of the Diapsida. Manus 2, 3, 4, 5, 3, and pes 2, 3, 4, 5, 4. 



The suborder Pelycosaiiria is of special interest, as it illustrates perhaps 

 better than any other group known the stages in the advancing special- 

 ization of structure from a comparatively generalized skeleton to an 

 organization that was possibly the direct cause of extinction. The more 

 primitive forms of the family Poliosati rides closely resemble the Protero- 

 saiiria. 



•students of this paper are requested by the author to read first the morphological description of 

 Dimelrodon iticisivus, p. 95. This is the best-known form of the suborder and has been described as fully 

 as possible. In the description of other members of the group comparison has been made as uniformly as 

 possible with Dimetrodon incish'us, and the scheme of classification will be best understood after a study 

 of the osteology of this typical form. 



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