90 REVISION OF THE PELYCOSAURIA. 



rises from high on the side of the neural arch ; it is short and projects almost straight 

 out. The side of the articular edge of the centrum is rounded as if for the beginning 

 of a capitular facet. The base of the neural arch is elongate autero-posteriorly, 

 between the zygapophyses. 



The last iu'o himhars are notably different from Diinetrodon and show the chief 

 distinguishing characters of the genus. 



The centra are exceptionally short with deeply concave sides and bottom line. 

 The bottom line is wide and rounded. The portion of the face surrounding the 

 intercentrum is nearly circular, but on both the anterior and posterior faces there is a 

 wide extension of the face below the intercentrum forming a flat face nearly as wide 

 as the portion above. These faces are not bent back as are the intercentral faces of 

 the anterior dorsals of Dinietrodon and seemingly fitted closely together leaving no 

 space for an intercentrum, which probably underlay the line of meeting of the two. 



Measttremenls. 



mm. mm. 



Length bottom line of axis 23 Diameter of anterior face of centrum of same: 



Diameter of anterior face of centrum of same: Vertical 24.5 



Vertical 25 Horizontal 21 



Horizontal 19 Length bottom line of second presacral 13 



Length bottom line of : Diameter of anterior face of centrum of same: 



Anterior dorsal (anterior face crushed) 22 Vertical 22 



Posterior dorsal 21 Horizontal 21 



Diameter of posterior face of centrum of same: Length bottom line of first presacral 11 



Vertical 23 Diameter of anterior face of centrum of same : 



Horizontal 17 Vertical 26 



Length bottom line of a lumbar (?) 19 Horizontal 21 



Family CLEPSYDROPIDAE Cope (see p. 36). 

 Subfamily CLEPSYDROPINAE Case (see p. 37). 



Genus CLEPSYDROPS Cope (see p. 37). 



The single well-known and determinable species is Clepsydrops natalis. 



The description of the genus is embodied in the discttssion of that species 



below. 



Clepsydrops natalis Cope (see p. 42 and plates 4, 5, and 6). 



Clepsydrops collctti Cope, partitn, p. 40. Clepsydrops vinslovii, partim, p. 42. 



Characteristic specimens: No. 41 10 American Museum, the type. No. 41 11 

 Am. Mus. Nat. Hist., Cope, coll.: A pelvis with femur in position (plate 6). No. 2290 

 Am. Mus. Nat. Hist, Cope, coll.: A front foot lacking carpale i and metacarpale i. 



The type specimen, No. 41 10 American Museum, has been repeatedly described 

 (Cope 44, Case 29) so far as the conditioii of the specimen permitted, but in the prep- 

 aration of this description the refractory matrix which previously obscured many points 

 has been completely removed ; for this reason previous descriptions are disregarded and 

 a complete redescription given. 



The skull (plate 4, figs. 7, 8) was high and narrow; this appearance is empha- 

 sized by the crushing of the specimen from side to side in fossilization ; probably it 

 was not so high and narrow as in Dimctrodon incisivus. The condition of the speci- 

 men makes it impossible to trace all of the sutures in the skull, but it is evident that 

 the skull was closely similar to that of Dhiietrodon and that the bones were of the same 

 form aud general relations. The posterior temporal region is badly crushed. 



