9 6 



what recurved, and tapers towards the upper extremity, which 

 is marked by a smooth rounded facet for the cartilaginous 

 supra-scapula. The pre-coracoid is long, sub-cylindrical at its 

 origin, but becomes broad and flat distatly ; at the extremity it 

 is longitudinally striated. The proximal end is flexed forward 

 at an obtuse angle, and is expanded to form the long suture 

 with the scapula and coracoid. It contributes considerably 

 to the glenoid cavity. The coracoid is remarkably long, and 

 after leaving the sutures with the other elements of the girdle, 

 becomes very broad and thin. This is most marked distally. 

 The anterior border is thickened, and the bone is slightly 

 concave on both surfaces. 



The three parts of the shoulder girdle are united by dis- 

 tinct bony symphyses ; they differ from some of the modern 

 species, in which there is only a ligamentous union between 

 the coracoid and the other parts. It presents a further differ- 

 ence in the long and slender neck which is formed by the 

 flexing of the pre-coracoid, and in the shallow and sub-circular 

 glenoid cavity. The short scapula and long coracoid would 

 indicate a species with a low, broad carapace, as was probably 

 the case in E. wyomingensis, though much difficulty has been 

 experienced in determining this point, owing to the distortion 

 of the specimens. 



Measurements. 



M. 



Length of neck to point between coracoid and precoracoid 0345 



Length of coracoid (about) ^ -133 



Length of precoracoid 1 14 



Length of scapula (about) 126 



BAENA, Leidy. 

 BAENA UNDATA, Leidy. 



Cont. to Ex. Vert. Fauna, p. 160. 



Three nearly perfect shells of different ages, from Dry and 

 Cottonwood Creeks. 



TRIONYX, Geoffr. 

 TRIONYX UINTAENSIS, Leidy. 



Cont. to Ex. Vert. Fauna, p 176. 



Cottonwood Creek. 



