24 REVISION OF THE PELYCOSAURIA. 



In 1892 Cope formed the genixs Diopciis for the specimen previously 

 described as C. leptocephalus, since he had discovered in it the presence of 

 two temporal arches. 



" In Diopeiis Cope the supratemporal region is elongate in the vertical direction, 

 and as elsewhere it overlaps the quadrate at the distal extremity. Anteriorly it sends 

 forward a process probably for union with the postorbital bone, which is, however, 

 entirely free from the parietal and incloses a foramen with it, precisely as in Sphen- 

 odon. It further resembles the corresponding element in Sphenodon in sending 

 upwards a branch for union with the parietal. There are in this genus two posterior 

 bars and two foramina, thus differing widely from the other Permian genera of this 

 or any other country known to me. Whether it has a free parieto-quadrate arch I do 

 not know, but it is probable that the genus should be referred to the Rhynchocephalia 

 in the neighborhood of Palaeohatteria Credner. It differs from Sphenodon and 

 resembles closely the Theriodoniia in the absence of an obturator foramen, and in the 

 character of its dentition. The zygomatic arch is not excavated below, but has a 

 straight outline to its junction with the jugal. The quadrate condyle is double like 

 that oi Sphenodon and the Clepsydropidcs:' 



Revised description of the genus : 



(i) No well-defined diastemal space; the faint notch between maxillar>' and 

 premaxillary filled with teeth. 



(2) A single well-defined maxillary canine ; incisor teeth enlarged. 



(3) Section of teeth at base quadrate. 



(4) Neural arch coossified with centrum in adult. 



(5) No great change in length of vertebrae in different parts of the column. 



"As deep as long in all parts of column if measured at center." Poste- 

 rior lumbars not greatly shortened ; without wide intercentral face. 



(6) Anterior dorsals without wide face on lower part of anterior face of cen- 



trum for the intercentnim ; without median keel. 



(7) Character not shown. 



(8) Spine of axis not elevated and broad at top. 



(9) Limb bones without well-developed articular faces. 



(10) Character not shown. 



(11) Abdominal ribs or scales absent ? (not observed). 



(12) Tail long. 



(13) Elongate, slender body, probably from 2 to 2.5 meters in length. 



The specimen was originally described as belonging to the genus 

 Clepsydrops ; Cope, believing at the time that Clepsydrops had but a single 

 temporal arch and fenestra, compared it directly with the Theriodonts of 

 Africa ; when he determined that it had a double arch he removed it to a 

 new genus, Diopeus. The discovery that the Clcpsydropidce are all diap- 

 sidan removed the main distinction of Cope's classification, but other char- 

 acters, as listed above, justify the distinction of the genus. 



