'rUB MOST PRIMITIVE KNOWN REPTILE. 



281 



Tlie ribs on the 4th and 5th caudals ar.e very distinctly double- 

 headed, having a distinct emargination between the well-marked 

 tuberculum and capitulum. This feature is, I believe, known in 

 no other vertebrate. 



Text-fle-ure 10. 



FPr.Cor, 



Seijmouria hayloriensis Broili. — Outer surface of the incomplete riglit scai'ula 

 aud precoracoid, X f . 



The fr.agment lying on the anterior end of the coracoid is clavicle. 



Eeference letters; — Cl., clavicle ; F.Gi., glenoid foranaen ; F.Pe.Coe., precoracoid 

 foramen; F.S.Gi., supra-glenoid foramen ; Pe.Coe., precoracoid ; Sc, scapula. 



Shoiolder- girdle. — The shoukler-girdle has already been well 

 described by Broili and Williston, but some features of its 

 structure have so far escaped observation and others are worth)' 

 of further emphasis. The scapula is exactly a,s Williston has 

 described it, with a veiy broad supra-glenoid fossa, high up in 

 which lies the small supra- glenoid foramen. My specimen shows 

 clearly not only that it only ai'ticulates with a single coracoidal 

 element, but also that it differs from the somewhat similar con- 

 dition in . Varanoojjs in not presenting an articular face for a 

 cartilaginous posterior coracoidal element. In fact the evidence 

 makes it quite plain that there was only a single coracoid, 

 corresponding to the anterior one of most Ootylosaurs, the 

 posterior not being represented even by a cartilage. The pre- 

 coracoid is as Williston has described it, with a very deep fossa, 

 on its outer surface behind . the front of the glenoid cavity. A 

 small glenoid and a much larger precoracoid foramen open into 

 the fossa. 



The glenoid cavity is represented by a deep groove, V-shaped 

 in section. This groove during life must have been filled up 

 with cartilage, its margins map out a typical screw-shaped glenoid 

 articulation. 



Sternum. — The hard matrix lying on the inner surface of the 



