SYSTEMATIC REVISION 23 



superior border depressed as in D. phaseolinus. The interorbital space is gently 

 convex, and is wider than the diameter of the eye, but how much wider the state of 

 the specimen leaves uncertain. The jugal bone is quite narrow below the orbit, 

 its vertical diameter equalling two-fifths that of the latter. The surface of the 

 cranium is rather minutely wrinkled, and does not display the grooves seen in the 

 Diadectes latibuccatus. The tabular bone forms a rounded and narrowed cap of the 

 posterolateral angle of the skull, and is much less prominent than in the genus 

 Chilonyx, but more so than Diadectes, where it is not distinguishable by suture. 



"Measurements. 



"Total length of the cranium from the pre- M Diameters of fifth tooth: M 



maxillary to the os tabulare inclusive . 0.284 Longitudinal 0.015 



Diameters of the nostril: Anteroposterior 007 



Vertical 025 j Transverse 010 



Transverse 033 j Diameters of the twelfth tooth : 



Distance from nostril to orbit 078 ! Longitudinal 013 



Diameters of orbit: Anteroposterior 0065 



Vertical 053 ; Transverse 013 



Tran verse 054 Diameters of the sixteenth tooth: 



Interorbital width (posterior to middle) . .070 j Longitudinal OIO 



Length of dental series (chord) . . . .150 Anteroposterior. • 005 



Transverse 00 %5 



"The dimensions of this skull are equal to those of Diadectes phaseolinus, and 

 about one-fourth larger than those of Diadectes latibuccatus. The bones of the 

 cranium are thinner and lighter than those of any other species of the family that 

 has come under my observation." 



Revised description of the genus and species: The genus and species is based on 

 a single lateral half of a skull; no other specimens are known. Closely related to 

 Diadectes, it is distinguished by the greater thinness of the bones of the skull and the 

 less rugose sculpture of the surface. The differences in proportions, from Diadectes, 

 may readily be accounted for by the conditions of preservation; most of the skulls of 

 Diadectes have been preserved more or less entire and have been subjected to pressure 

 from above ,; d own ward, the skull of Bolbodon was split in the median line before 

 fossilization''and "subjected to lateral'pressure. The tooth figured by Cope is the 

 posterior one of the series and is not characteristic; in all of the species of Diadectes 

 the posterior tooth is smaller and more simple than the more anterior ones. 



Genus CHILONYX Cope. 



Bolosaurus rapidens Cope, Proc. Am. Phil. Soc, vol. XVII, 1878, p. 507. 



(Also Pal. Bull. No. 29.) 

 Chilonyx Cope, Proc. Am. Phil. Soc, vol. XX, 1883, p. 631. 



Trans. Am. Phil. Soc, vol. xvn, 1892, p. 13. 



Proc. Am. Phil. Soc, vol. xxxiv, 1896, p. 441. 



Proc. Am. Phil. Soc, vol. xxxv, 1896, p. 131. 



Type: An imperfect skull. No. 4357 Am. Mus. Nat. Hist. Cope Coll. From 

 Texas. 



Original description: "Teeth with the long diameter of the crowns transverse 

 to that of the jaws, and with the crown contracting to a single slightly incurved apex. 

 Maxillary series of teeth short. Temporal fossae overroofed. Superior surface of 

 the cranium divided into more or less swollen areas by grooves. 

 "^Tt'The single species of this genus is one of the largest saurians yet obtained in 

 the Permian of North America." 



