Case: Vertebrate Fossils from Pittsburgh, Pa. 



237 



O^CP 



e -/ i f 



Fig. 5. Teeth of various '^.Diadectids and 

 related forms, a, Bolbodon ; b, Bolosaurus ; 

 c, Desmatodon ; d> Diadedes ; e, Diadectes ; 

 y, Empedias. 



The inner side of the apex is nearly vertical and presents a flat face in- 

 wards, this more prominent on the posterior and largest of the teeth than 

 on the anterior ones. The surface of the crown is marked with fine lines 

 and the sides of the root show the same character, but here the lines 

 are coarser. The inner half of the crown of the anterior and the 

 posterior teeth shows no wear, but on the two in the middle there are 

 surfaces worn by attrition on 

 both the inner half of the crown 

 and on the apex. The relation 

 of this genus to its nearest re- 

 lated forms is indicated in the 

 figure here given (Fig. 5). 



It has recently been shown 

 (Case 1907) that Bolosaurus is 

 a member of the reptilian group 

 Synaptosauria, but it is prob- 

 ably nearer to the Pariotichidae 

 than the Chelydosauria, so that 

 the intermediate forms of the teeth of Desmatodon may indicate rather 

 a stage of adaptation to food supply than a step in a phylogenetic 

 series. The teeth of the Diadectids are so character- 

 istic in form that their discovery is especially fortunate, 

 as it places beyond any doubt the correlation of this 

 fauna with that of Texas. 



There are seven chevron bones preserved (Fig. 6) ; 

 they all have the characteristic form already described 

 (Case 1903). The upper portion is nearly semicir- 

 cular and the articular face is divided into two por- 

 tions which lie nearly at a right angle to each other, 

 so that the shaft of the bone, in its natural position, 

 with the articular faces interposed between the lower 

 edges of the articular faces of two adjacent vertebrae, 

 was nearly parallel to the tail. The distal portion of 

 the bone is comparatively long and the extremity is 

 somewhat flattened from side to side. The largest of 

 the chevrons is .051 m. in length, which indicates an 

 animal from four to five feet long. 

 Pelycosauria. — A small fragment of what is evidently a neural 

 spine gives evidence of the existence of a new member of this sub- 



Fig. 6. Chev- 

 ron bone of a 

 Diadectid. \. 



