part 3] TROM THE WEALD CLAT OF BERWICK (STJSSEX). 293 



posterior border of the interclavicle, behind which they seem to 

 have met in a median sutm'e. Their thin posterior edge is strongly 

 concave ; towards their outer ends they become thickened and 

 bent sharply upwai'ds, the convex surface thus produced fitting 

 closely into the shelf -like projection on the inner side of the scapula 

 (as described above). Apparently the posterior ends of the united 

 clavicles overlapped the upper surface of the anterior ends of the 

 forward prolongations of the coracoids, thus closing a large 

 fenestra bounded by the coracoids, scapula, and clavicles. 



The dimensions of this shoulder-girdle (in millimetres) are as 

 follows : — 



Greatest length of tlie whole girdle as mounted 426 



Width of the same at the glenoid cavity 278 



Coracoid. 



Greatest length 332 



Width at the glenoid prominence 153 



Least width of anterior prolongations 30 



Width of anterior ends of the same 45 



Length of glenoid facet about 70 



Depth of the same 37 



Length of scapular facet 39 



Greatest depth of symphysial surface about 28 



Scapula. 



Greatest length of ventral ramus 150 



Width of the proximal end 61 



Width of neck about 37 



Length of the upper border of the dorsal ramus 193 



Greatest width of the anterior border of the ventral ramus. . . 81 



Clavicular arch. 



Greatest width of the arch as a whole 218 



Antero-posterior length of the same in the middle line about 125 



Width of interclavicle about 140 



Greatest width of left clavicle 135 



This type of shoulder- girdle seems to be a primitive one, being 

 very similar to that of a girdle from the Lower Lias of Street 

 (Somerset) which is represented in the text-figure (B, p. U95). 

 This is part of the type-specimen of Plesiosaurtis arcuatus^^ 

 tigured in Hawkins's 'Sea-Dragons' (1834) and described in part by 

 E-ichard Owen in the British Association Report on Fossil Keptiles 

 for 1839 (1840) p. 76. This skeleton, which is in the British 

 Museum (Natural Historv), was registered under several numbei*s 

 (2028*-29*, E. 1317-18/, and it is only recently that the bones 

 of the shoulder-girdle have been developed and mounted with the 

 advice of Prof. D. M. S. Watson. As now figured (text-fig. B), 

 it is one of the best specimens of the shoulder- girdle of a 

 Liassic Plesiosaur known. The clavicular arch has already been 

 described and figured in detail by H. Gr. Seeley.^ In its general 

 structure it is very similar to that described above ; but the inter- 

 clavicle {i.cl.) is wider, and the concavity of its anterior border 



^ Referred below to the new genus Eurycleidus. 



2 Proc. Eoy. Soc. vol. U (1892) pp. 128-30 & text-figs. 2-3. 



Q. J. O. S. No. 311. X 



