462 PROF. W. J. SOLLAS ON A NEW SPECIES OF PLESIOSAUEUS 



indicate this ; hence a possibility to be borne in mind in making 

 specific determinations of isolated bones. 



The Radius. 



The right radius is a straight, almost parallel-sided bone, elliptical 

 in transverse section, truncated by slightly convex ends ; it has a 

 simpler outline than is usual in Plesiosaurs. The left radius, which 

 has suffered more from compression, has more of the usual Plesio- 

 saurian outlines : its outer edge is gently concave, its ulnar margin 

 tricurvate, the middle curve being concave inwards ; and its once 

 cartilaginous articular surfaces have been squeezed beyond the edge 

 of the flat surface of the bone. It is much ridged longitudinally, 

 the ridges diverging a little from the middle towards the ends. 



Representing the length of the humerus by 100, that of the radius 

 will be 37 ; and this number may be called the humero-radial index. 

 Its value for other species is found in the table on page 477. For 

 P. rostratus it will be seen to be almost the same as for P. Cony- 

 beari. 



Dimensions of Humeri, Radii, Ulnce, and Femora. 





Diameter of 



Diameter at 



Diameter of 



Len 



gth 





head. 



middle of length. 



distal p,nd. 









































from 



from capi- 





















Ea. Ul. 



A. P. 



Ea. Ul. 



A. P. 



Ea. 



Ul. 



A- P. 



end to end. 



tular ridge 





















to end. 





















Humerus : — 











chord. 



arc. 









Eight 



3-5 



2-9 



3-9 



2-0 



6-7 



8-2 



1-2 (?) 



14-8 



15 A. 

















14-25 P. 



Left 



(?)36 



3-2 



3-9 



20 





•55 





14-8 



14-8 P. 



Femur : — 



















Eight 



35 



3:6 



34 



20 



6-7 





1-2 



14-25 



12- 75 M. 



13- 5 A. 



Left 



3-5 



3-8 



37 



1-6 







1-2 



14-37 



13-37 



Eadius : — 





















Eight 







3-6 





3-5 



3-75 



07 



5-45 





Left 



3 : 9 



0-8 



3-15 



0-55 



3-5 



3-5 



0-55 



50 



4-75 



Ulna:— 





















Eight 



2-8 





39 





4-85 



6-5 



0-7 



5-5 





Left 



2.8 



6 ; 7 



37 





47 



6-0 





5-6 





Ea. Ul. means from radial to ulnar margin ; A. P. means from anterior to 

 posterior margin ; Chord means measured along chord of curve; Arc means 

 measured along curve itself. In the last column A., M., P. mean measured to 

 anterior, median, and posterior edge of distal margin respectively. 



The Vina. 



The right ulna, like the right radius, retains more of its original 

 form than the corresponding bone on the left ; for although its distal 

 two thirds are much flattened, its proximal third still presents its 

 original thickness. 



This uncompressed portion has a smoother surface than the other, 



