1893.] Clavicular Arch in Ichthyosauria and Sauropterygia. 157 



the coracoid ; and by " homology " I mean thafc, since the coracoid 

 foramen is not in the middle of the coracoid bone, the Ichthyosaurian 

 coracoid is not homologous with the Lacertilian coracoid ; and, since 

 this foramen in Ichthyosaurus is not denned by the coracoid and 

 scapula, but could only be completed by a structure which occupied 

 the open angle between the coracoid and scapula, the coracoid is 

 not homologous with that of Saurischia or Ornithischia ; and can 

 only be compared with the coracoid of an animal in which a separate 

 precoracoid is developed. I had not realised that this was a con- 

 uon on which comparative anatomists have been in accord. 



FIG. 6. Shoulder girdle of Nothosaurus mirabilis restored. I.C., interclavicle ; 

 Cl., clavicle ; Sc., scapula; cor., coracoid;/, coracoid foramen; ? pc., 

 hypothetical cartilaginous precoracoid. On the left side this element 

 (?) is represented as possibly extending along the clavicle, as in Ornitho- 

 rhynvhus and Ichthyosaurus. 



I have also advocated the identification of the precoracoid as bring- 

 ing the shoulder girdle of Ichthyosaurus into harmony with that of 

 Nothosaurus, because in that genus there is a similarly incomplete 

 coracoid foramen, and similar internal cartilaginous surfaces truncat- 

 ing the coracoid anteriorly and the scapula internally so as to include 

 an angle between them, which such a cartilaginous precoracoid would 

 occupy, so as to complete what I regard as the coracoid foramen, I 

 only know the Nothosaurian shoulder girdle from von Meyer's 

 excellent figures, and in contesting my interpretation I do not gather 

 that Mr. Hulke has better knowledge of the original materials. It is 

 urged that I am in error in identifying the coracoid foramen of 



