22 A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA 



end only very slightly overhangs the lower. In Diadectes the face is inclined 

 sharply downward and forward. In the more anterior vertebrae the face on the 

 transverse process grows in length, but the process itself remains so short that it 

 may almost be considered as absent and the articular face attached to the posterior 

 surface of the anterior zygapophysis. 



Measurements. 



mm 



Transverse diameter of a centrum at the middle . 23 



Transverse diameter of the same at the bottom . 12 



Anteroposterior diameter of same 20 



Height of same vertebra to the base of the spine 63 



Width across the posterior zygapophyses 66 



Width across zygapophyses anteroposteriorly 37 



Genus BOLBODON Cope. 

 Proc. Am. Phil. Soc, vol. xxxv, 1896, p. 134. 



Type: Half of a skull, showing only the dermal bones of the roof. No. 4373 

 Am. Mus. Nat. Hist. Cope Coll. From Texas. 



Original description: "Molar teeth without external heel and with one median 

 cusp. Cranial bones coossified; no grooves indicating the sutures of dermal scuta. 

 Internal borders of the palatine bones in mutual contact, and dentigerous. 



"The dentition of the genus is not different from that ot Phanerosaurus, as 

 described and figured by Geinitz and Deichmuller. In that genus, according to the 

 authors, the cranial elements are distinct, the sutures being persistent. In Bolbodon 

 the cranial elements are entirely coossified, excepting only the tabular bone, which 

 is distinguishable. The nostril is large, and a turbinal bone is visible within it as 

 in Pariotichus. The lateral and inferior bones of the brain case, and the mandible, 

 are not preserved." 



Bolbodon tenuitectus Cope. (Plate 10, fig. 1.) 

 Proc. Am. Phil. Soc, vol. xxxv, 1896, p. 134. 



Type: Same as the genus. 



Original description: "From the middle line at the apex of the vomer to the 

 posterior extremity of the maxillary bone there are alveoli for seventeen teeth. Of 

 these, six only are occupied by teeth, which are Nos. 5, 7, 10, 12, 13, 16. Of these 

 only 5, 13, and 16 have perfect crowns. The skull has been somewhat distorted by 

 pressure, so that the longer axis of the roots and crowns are somewhat oblique to 

 their correct positions. The roots of Nos. 5 and 7 are wide oval in section, and the 

 long axis becomes longer posteriorly up to No. 16, in which it is a little contracted, 

 and where the entire dimensions are smaller. The crown of No. 5 is caniniform and 

 acute (the crown of this tooth is missing in the present condition of the specimen), 

 is curved backwards as to its anterior face, and has a worn posterointernal face 

 due to the opposing tooth of the inferior series. In No. 13 the crown is much more 

 expanded transversely, and the external border is convex medially and incurved 

 above and below. Curved shallow grooves radiate from the external (?) apex down- 

 wards and inwards. The crown of the sixteenth tooth is cordiform, with the acute 

 apex upwards. Shallow grooves descend from the latter. Like the maxillary 

 teeth the palatines are widely spaced. The sections of their crowns are a wide oval 

 placed longitudinally; apices lost. 



"The nostril is large and is rounded subquadrate. The orbit is large and is 

 subround, and its border is not notched as in the Diadectes latibuccatus, nor the 



