MORPHOLOGICAL REVISION 97 



posteriorly they diverge and receive between them the anterior ends of the ptery- 

 goids. There is no trace of teeth on the prevomers. On either side are the elongate, 

 oval openings of the posterior nares. 



The palatines lie in the normal position, but the sutures can not be clearly 

 made out; the posterior end seems to be marked by a suture extending inward and 

 backward from a point about opposite the middle of the orbit. A short row of small 

 teeth extending outward and forward from the median vacuity seems to be confined 

 to the palatine. 



The pterygoids have the usual tripartite form. The posterior process is a thin, 

 nearly vertical, plate extending back to the quadrate and is applied to its inner 

 surface. A strong basisphenoid process joins the basipterygoid process of the basi- 

 sphenoid. In the type specimen of C. aguti the palate has been very slightly crushed 

 together from the sides, so that the basisphenoid processes lie between the basi- 

 pterygoid processes of the basisphenoid and the interpterygoid vacuity is narrowed. 

 This may also account for the loss of the parasphenoid rostrum in this specimen. 

 The external processes of the pterygoid extend out to the maxillary and there is no 

 trace of an ectopterygoid bone. The posterior edge of the external process is prom- 

 inent and the outer end is lower and presents a terminal face to the lower jaw, as in 

 the Crocodilia, Sphenodon, and the Pelycosauria. The outer portion of this process 

 supported a small cluster of minute teeth. The anterior processes are long and slender 

 and extend far forward between the palatines and prevomers. The inner edges 

 anterior to the basisphenoid processes are concave and surround a considerable 

 interpterygoid vacuity; opposite the anterior end of the orbit the inner edges of the 

 pterygoids come in contact. From a point opposite the palatine suture the inner 

 edge of the pterygoid supports a single row of small teeth. 



3 The basisphenoid is exceptionally elongate, with a deep groove on the ventral 

 surface. The presence of foramina for the internal carotid arteries can not be made 



out. 



The paroccipital is distinct and extends out to the quadrate; as in Labidosaurus, 

 it comes in contact with the outer of the two vertical plates on the posterior surface 

 of the skull, the quadratojugal. 



The lower jaw shows the angular, surangular, splenial, and dentary; the other 

 bones are not visible in any of the specimens. The dentary supports a cluster of 

 teeth arranged in three irregular rows. The teeth are obtusely conical, as in the 

 upper jaw. The anterior teeth are concealed by the overhanging maxillary in the 

 type specimen of C. aguti, but in others it is seen that the first three were consid- 

 erably larger than the others. The third is especially large and fits into the notch 

 formed on the upper series by the reduction of the posterior premaxillaries and 

 the anterior maxillaries. The splenial passes forward and takes a strong part in 

 the symphysis. The angular and surangular extend back of the articular region 

 and form a strong pointed projection at the rear of the jaw. 



The interclavi cle has a broad rhomboid head with a slender posterior prolonga- 

 tion; the end of this is broken away, so that it is impossible to give the exact length. 



The clavicles have flat anterior ends lying upon the interclavicle and expanded 

 parallel to it; the distal ends are expanded, but at a right angle to the proximal ends, 

 so that while the proximal end was horizontal the distal end was vertical. 



The scapulce have not been made out sufficiently to give a figure. Williston 

 (67) in his description of Captorhinus isolomus (P. laticeps) speaks of the shoulder 

 girdle as follows: "It is very certain that the girdle was attached immediately back 

 of the skull, the front part underlying the occipital condyle even. Its structure is 

 almost identical with that of Labidosaurus, as figured by me (see fig. 47, c). I find 



