METRIOEHYNCHUS. 173 



The propodial bones are flattened and disc-like, so that, as in Geosaurus, the fore 

 limb was modified to form a paddle-like structure. This was first recognised by 

 E. Auer*, who described a disc-like bone as a propodial, but was unable to be sure 

 whether it was a radius or ulna : this specimen belonged to a skeleton from the Oxford 

 Clay collected by Mr. Leeds. In the present collection there is one specimen of the 

 fore limb in which both the propodials are preserved, but unfortunately no information 

 as to their exact position with regard to one another and to the humerus is available. 

 Indeed, it is not even possible to be sure which is the radius and which the ulna. 

 Examination of the bones themselves and comparison with the corresponding elements 

 in the fore limb of Geosaurus gracilis (see frontispiece, the figure given by Ammon f , 

 and text-fig. B in the Introduction) suggest that the arrangement shown in text- 

 fig. 70, A, is probably the correct one. The bone regarded as the radius (r.) is an 

 oval disc, thin except at the postaxial side of its proximal end and at its distal 

 extremity, where there are thickenings bearing convex surfaces, that at the proximal 

 end being the larger and probably representing the articular surface for the humerus. 

 The ulna (u.) is an irregular trapezoidal plate of bone, thickened at the preaxial side 

 of its proximal end, where there is a surface presumably for union with the humerus 

 and radius. Distally the oblique lower border is likewise thickened and no doubt 

 united with the proximal carpals, also disc-like in form. This extreme modification 

 of the fore limb is very similar to that described by Eraas J and Ammon § in the 

 case of Geosaurus and is further evidence of the extreme change undergone by 

 members of this group in relation to their pelagic life. 



The rest of the fore paddle is unknown, but a small bone figured by Arthaber || 

 as the first metacarpal, and perhaps the carpals figured by the same author, may actually 

 belong here. 



Pelvis (text-figs. 71-72). — The ilium (il.), which considering the large size of the 

 hind limb is comparatively small, differs very much from that of Steneosaurus 

 (of. text-fig. 43, p. 109, & text-fig. 44, p. 111). Thus the dorsal border running back- 

 wards from the antero-superior angle (a.a.) is short, and so also is the posterior 

 border, which makes a very obtuse angle with the dorsal, the whole of that part of 

 the bone corresponding to the postero-superior corner of the ilium in Steneosaicrus being 

 wanting. At the same time the anterior border is very long, so that the acetabular 

 border, instead of being nearly parallel with the dorsal edge, makes an angle of about 

 40° with it, sloping upwards and backwards. The outer surface of the bone is concave 

 and much roughened, particularly in the neighbourhood of the thickened anterior 



* -'Die Extremitiiten von Metriorliyncliw" Centralbl. f. Min. etc. 1907, p. 536. 



t Geognostische Jahreshefte, vol. xviii. p. 07 (Miinchen, 1905). 



% Palaeontographiea, vol. slix. (1902) p. 5(i, pi. viii. fig. o. 



§ Geognostische Jahreshefte, vol. xviii. p. 07 (Miinchen, 1905). 



U Beitr. Palaont. Oestsr.-Ung. vol. xix. (1900) pi. xxv. figs. 11 a,b,c; also figs. 10 & 12. 



