Apr. 1903. North America** Pl esiosai rs — WillIston. 29 



the parietal, is elongate oval in shape, slightly convex in both direc- 

 tions, and turned obliquely inward posteriorly, so that the two bones 

 when in place form a V. The surface looks forward and upward, and 

 joins a projecting sutural surface of like shape on the parietal bone. 



Mandible. — From the exterior of the mandible four elements are 

 visible, arranged much as in the crocodile or Sphenodon. The dent- 

 hi \ extends far back along the upper border, quite to the top of the 

 coronary eminence. Thence its suture runs obliquely to a little 

 beyond the posterior end of the symphysis on the lower border. The 

 element back of this on the upper border is doubtless the surangular. 

 separated from the angular below by a suture placed very much as it 

 is in the crocodile, beginning at the extreme posterior end of the 

 mandible. The bone extends anteriorly as an elongated point between 

 the dentary above and the angular below. The suture separating the 

 element from the articular cannot be made out. The two, united, 

 agree quite with the element described by Guenther in Sphenodon, and 

 as seen in a specimen fifty-eight millimeters in length before me. 1 

 distinguish in this mandible, as did Guenther in his, only four elements 

 — the dentary, which reaches far back; the coronoid, a flat triangular 

 bone occupying its usual place; the articular, inclusive of the 

 surangular; and the angular. Baur* describes five elements in a 

 Sphenodon skull fifty-six millimeters in length. The articular he 

 restricts to a small nodule or disk oi bone, similar to that of the 

 turtles, forming the articular surface; the surangular, the bone 

 before the cotylus, which he indicates as separated by a suture; the 

 angular he considers to be the inner prolongation of the bone which 

 reaches to the coronoid. The slender bone usually called the angular 

 he believes to be the splenial; while the bone usually called the 

 splenial (presplenial, Baur) in the crocodile and lizard he believes to 

 be wanting in the Sphenodon, as it usually is in the turtles. The 

 small ossification which he finds in the cotylus of the young 

 Sphenodon, similar to the element in a like place in the Tesfudinata, he 

 assumes to be present in all reptilian mandibles, but is obliterated in 

 the adult skull by the anchylosis of the suture. I certainly do not 

 find such a bone in the Sphenodon mandible before me, nor could Guen- 

 ther distinguish such an element. He believes then, that the element 

 usually considered the articular, is in reality composed of two bones — 

 a chondrogenous articular part and a dermogenous anterior prolonga- 

 tion. This is probably true, but I do not see the necessity of chang- 

 ing the names of the other anterior elements and of calling this 



* American Naturalist, 1891. 



