1869.] HTJLKE KIMMEEIDGE-CLAY SAITRIAN. 389 



Owen), and it is the bone on which Mantell founded his genus 

 Pelorosaurus. But the agreement is not complete ; for, besides the 

 much greater size of the Pelorosaurian humerus, which cannot be 

 altogether explained by assuming the bones to have belonged to 

 individuals of different ages (because the smoothness and compact 

 texture of the Kimmeridge bone, and the absence of the large 

 and numerous vascular foramina so conspicuous near the articidar 

 end in young and growing crocodiles, show it to have belonged to an 

 adult animal), there are variations of details, amongst which I may 

 cite the very different form of the transverse sections of the shafts 

 and the presence of a medullary cavity in Pelorosaurus. 



We have, then, in this humerus evidence of the existence during 

 the Kimmeridge period of an immense saurian fitted for terrestrial 

 progression, with strong crocodilian affinities, but differing from any 

 yet completely known to us ; of such a gigantic saurian we had 

 already traces in a great ungual phalanx from the Kimmeridge 

 clay of Ely and a fibula from near Weymouth, both in the British 

 Museum, and in a cast of a large tibia also in the same collection, 

 the original of which I think I have seen in the Woodwardian 

 Museum labelled " Macrochelys^'*. 



Measur €17167118. 



inches. 



Length 31 



Girth of shaft at a 13 



Proximal end: — 



Length of terminal surface along the curve 11 



Maximum width of terminal surface 4*5 



Width near anterior angle 1'5 



„ at posterior angle 1 



Girth 21 



Direct line between anterior and posterior angles of terminal 



surface 8 



Distal end : — 



Girth 24 



Transverse diameter of terminal surface 9 



Width (from upper to under surface) of posterior condyle ... 6 



„ of anterior condyle 3"5 



„ at intercondyloid notch 3 



EXPLANATION OF PLATE XVI. 



Left Saurian humerus from Kimmeridge Bay. In the Collection of J. C. 

 Mansel, Esq. 



[The fractions annexed to the figures indicate the extent of the reduction from 

 the natural size.] 



Fig. 1. Under (or anterior) surface: a, anterior (or outer) border; b, proximal 

 end ; c, distal end. 



2. Upper (or posterior) surface : a, posterior (or inner) border ; b, proximal 



end; c, distal end. 



3. Proximal terminal surface. 



4. Distal terminal surface : a, anterior ; b, posterior end. 



5. Transverse section of shaft, showing the absence of a medullary cavity : 



a, anterior, b, posterior surface. 



[* Mr. Seeley informs me that the name of" Gigantosaurus megalonyx" has 

 now been attached to this specimen. — W. S. D.] 



