192 MAEINE EEPTILES OF THE OSFOJRD CLAY. 



conditioa it appears that the posterior row of ventral ribs lay below the anterior portion 

 of the pubes. It seems probable that in life they were just in front of them, and that 

 the plastron with the shoulder-girdle and pelvis formed a complete bony armour on the 

 ventral surface of the body. The form and arrangement of the ventral ribs with regard 

 to one another in this specimen have been described above. In the fore paddles the 

 ulnas are very wide, and the postaxial portion of that on the left side, which is bent a 

 little downwards, seems to be on the point of separating off from the main body as an 

 accessory ossicle, traces of the line of division being clearly visible. On the right side 

 this part of the bone is already separate, though it remains in very close contact with 

 the remainder. Of course, these separate, or imperfectly separate, portions of the uln^ 

 may be interpreted also as accessory ossicles on the way to fusion with the main bone. 

 The dimensions (in centimetres) of this specimen are : — 



Basioccipital : length (approx.) 3'8 



width at pterj'goid processes 5- 4 



transverse diameter of condyle 2-6 



-rr J . Atlas and - Sixth 



VertebrEe • „ • i 



axis. cervical. 



Length of centrum in mid-ventral line . . . 5-0 3"2 



Width of posterior end of centrum S'i 4-0 



Height „ „ ,, 2'5+ 3-1 + 



The remainder of the cervicals and the other vertebrae are too much crushed to 

 supply measurements of any value. 



Hum.erus: length 34-1 



long diameter of head 9-5 



short ,, „ 6-9 



greatest width at upper end ]2-8 



width of shaft at narrowest point 7'6 



width of distal expansion 24-8 



Radius : length of preasial border 13-3 



„ humeral border 12-8 



TJlna: length 7"2 



width \vith postaxial portion 13-3 



„ without postaxial portion 12-0 



The pelvic bones are too imperfect to be measured. 



Femur: length 31-3 



diameter of head (exaggerated by crushing) .... 9'5 



greatest width at upper end 10-2 



width of shaft at narrowest 6-3 



,, distal expansion 18-6 



Tibia : greatest length 6-3 



„ width 9-0 



Fibula : greatest length 5-9 



„ width 9-0 



Length in mid-ventral line of plastron so far as preserved . . . 24-5 



Width (exaggerated by crushing) 78-0 



