THE PHYTOSAURIA OF THE TRIAS 141 



elements and hence their full anterior extent cannot be determined. 

 At their point of disappearance, however, they still maintain their 

 full thickness and must extend farther forward for some distance. 

 Viewed from below, the postero-lateral processes of the sphenoid, 

 the greater wings, form a high, transverse, rather sharp ridge 

 slightly depressed at the middle and somewhat thickened at the 

 extremities. This is about 76 mm. long and at the middle extends 



Fig. 7. — Angistorhinus grandls? Cojoined basioccipital and basisphenoid, 

 natural size. 



down 44 mm. below the lower edge of the presphenoid. The anterior 

 face of the pterygoid processes of the sphenoid reaches forward 

 about 35 mm. from this ridge and extends down about even with it. 

 These processes are quite stout and are separated from the posterior 

 wings by a narrow but deep channel. The posterior part of the 

 basisphenoid has been considerably abraded in this specimen and 

 a portion of the occipital condyle is missing. Another specimen is 

 present in the collection, however, a co-ossified basioccipital and 

 basisphenoid (see Fig. 7) that resembles this form very closely, and 

 this has aided materially in the interpretation of the specimen at 

 hand. On the posterior side of the transverse plate formed by the 



