. 



93.] Clavicular Arch in Iclithyosauria and Sauropterygia. 161 



anterior bone of the Plesiosaurian shoulder girdle in the way which 

 he represents by shading in his figure (fig. 8, p. 246) of the crushed 

 and imperfect Woodwardian specimen, which may be compared with 

 the figure given by myself in 1865 from a photograph, in the ' Annals 

 and Magazine Nat. Hist.,' series 3, vol. 16, PI. XV. In that specimen 

 there is a partial longitudinal division, which I believe may be better 

 explained by fracture. When the specimen was originally described, 

 Plesiosaurian clavicles had not been identified, and I thought the 

 division might represent a clavicle external to the scapula, and, 

 although that view became untenable with the discovery of the 

 clavicles in 1874 (' Quart. Jour. G-eol. Soc.,' vol. 30, p. 444), I have 

 since suggested that the ossification, if it ever were distinct, may 

 represent the epiclavicle (ec, fig. 2) which extends along the superior 

 margin of the scapula in Pareiasaurus Baini. It must be remem- 

 bered that in Plesiosaurus this supra-arthroidal process of the bone 

 is very thin, and ascends nearly vertically, so that it would be 

 peculiarly liable to fracture. The specimen is elucidated by no 

 other example in the separation and displaced position of the 

 ascending process of the scapula ; and, since it differs from other 

 specimens from the Lias only in the horizontal and displaced position 

 of that process, I have no doubt the specimen is delusive, in so far 

 as it appears to suggest two separate bones. If the bones had been 

 separate there would have been presumably a cartilaginous division 

 line between the two elements, if both entered into the formation 

 of the humeral articulation, in the position in which a division is 

 figured by Mr. Hulke, whereas there is no such indication of division 

 in the specimen, or in any other specimen. 



This crushed bone is insufficient to support and sustain a new read- 

 ing of the homologies of the great bones of the Sauropterygian 

 shoulder girdle. If there is no other objective evidence in the Plesio- 

 saurian skeleton, and Mr. Hulke mentions no other, there is, I 

 submit, no evidence in support of a precoracoid in the Sauro- 

 pterygia, except such as may result from comparison of Plesio- 

 saurian bones with those of other animals, since the division drawn 

 (' Roy. Soc. Proc.,' vol. 52, p. 246) is not in the line of fracture. 



I am in entire agreement with Mr. Hulke in comparing the 

 shoulder girdle of Sauropterygia with that of Chelonia, these orders 

 being grouped in the Sauromorpha, in the scheme of classification 

 given in 1891 ('Boy. Soc. Proc./ vol. 49, p. 520). The difference 

 between the views of Mr. Hulke and myself consists in the method 

 of comparison and its results. In Sauropterygia the bone in advance 

 of the coracoid which joins it by suture is in the same plane with 

 the coracoid. In the Chelonia the bone which has the same relation 

 to the coracoid is nearly vertical to the coracoid, or only inclined 

 slightly forward. The Chelonian bone consists of two slender rays, 



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