22 



NEW REPTILES AND STEGOCEPHALIANS FROM 



Other parts of the skeleton, but of these the majority are vertebrae and bones of the pec- 

 toral girdle; remains of limb-bones are scarcely represented m the collection, bome of 

 the isolated bones are described below. ^ ^, . ., , ,«•. , . , 



A nearly perfect left ramus of a lower jaw, No. 7469, University of Michigan col- 

 lection, was found by the author in the breaks of Sand Creek, just south of Cedar Moun- 

 tain The jaw lacks the extreme anterior end and the posterior end is somewhat crushed, 

 but the greater portion is in good condition. The length of the jaw is, allowing for the 

 missing anterior end, 43 mm., somewhat shorter than the jaw of -Bws^nma as indicated 

 by the skull. The jaw as preserved shows too great a curvature to be associated with 

 the skull in the same genus. The jaw is illustrated in figure 4, a and b. On the inner 



Fig. 4. 



A. Outer surface of left ramus of jaw of a large 



Stegocephalian, No. 7469, U. of Mich. 

 X 0.25. 



B. Inner surface of the same jaw shown in A. 

 dent., dentary; cor., coronoid; sur. ang., suran- 



gular; art., articular; sp., splenial; 

 pt. sp., postsplenial; ang., angular; 

 pr. art., prearticular. 



side there is a relatively large supra-Meckahan foramen and below this a surprisingly 

 large lower opening. The splenial is short and confined to the anterior fourth of the 

 ramus; it appears on both the inner and the outer sides of the lower edge and evidently 

 took part in the symphysis. The sutures marking the outlines of this bone are clear 

 and distinct. Posterior to the splenial there is a postsplenial which forms the middle 

 portion of the inner surface of the jaw; it appears on both the inner and outer sides of 

 the lower edge, but on the inner side rises in a smooth plate to form the greater part of 

 the inner surface. It is pierced by two good-sized foramina. The posterior edge of 

 the postsplenial extends back to the middle of the lower edge of the lower Meckalian 

 opening, where the suture is clear and distinct. From the middle of the upper edge 

 there is apparently a suture of irregular outline extending downward, but it can be traced 

 for only a short distance; the exact nature of this apparent suture can not be made out; 

 it may indicate the presence of an intercoronoid bone, but no other indications of either 

 an intercoronoid or a precoronoid can be detected. Posterior to the lower Meckalian 

 opening the inner surface of the bone is badly crushed and covered with a multitude of 

 small fracture lines which render it impossible to determine the course of any sutures. 

 It is altogether probable 'that the greater part of this surface is formed by the pre- 

 articular. The anterior edge of the supra-Meckalian opening is formed by the coronoid 

 and the prearticular; it is probable that the angular appears on the lower edge of the 

 inner surface, but the suture can not be made out. The coronoid extends forward in 

 a long process between the postsplenial and the inner edge of the dentary. The dentary 

 ends posteriorly in a sharp process between the coronoid and the angular or surangular. 

 Anteriorly it extends forward, forming the whole of the alveolar edge. The teeth are 

 small at the posterior end, but rapidly increase in size forward until they reach the 

 maximum size. Under the binocular microscope the structure of the teeth is seen to 

 be labyrinthine at the base, becoming much more simple near the apex. No teeth 

 appear upon the coronoid. 



