FROM THE LOWER LIAS OF CHARMOTJTH. 



465 



The Ischium (fig. 6). 



This " shoulder-of-mutton " shaped bone meets its fellow for about 

 half its length in the median symphysis. The ^-shaped anterior 

 margins of the two ischia meet to form together a bracket-like out- 

 line (■ — v ') ; the similarly shaped posterior margins of the pubes 



do the same ; and the brackets facing each other give rise to a 

 foramen, which is continuous from the pubic ischial smyphysis on 

 one side to that on the other. In this character the pelvis resembles 

 that of Mwcenosaurus, Seeley, Q,. J. G. S. vol. xxx. p. 206. 



The Ilium (fig. 7). 



The ilium has the usual Plesiosaurian form, a central shaft with 

 expanded ends, compressed in different planes, which are inclined at 

 about a right angle with each other. 



Fig. 7. — Diagram of Right Ilium. (Scale J.) 



Measurements of Pelvic Bones. 



Length of symphysis (fig. 6, ap) 5*5 



Breadth of bone from symphysis, and along a line at right angles to 



it, to anterior edge of acetabulum (ib. fl) 8*5 



Maximum antero-posterior diameter, drawn from d' 8*1 



Length of diagonal from inner anterior angle to anterior edge of 



acetabulum (af) 103 



„ from inner anterior angle to posterior edge of 



its share of acetabulum (a b) 103 



„ from outer antero-posterior to inner posterior 



angle (dp) 9 # 



„ articular surface for acetabulum (fb) 2*9 



,, „ ,, for ischium (b c) 2*3 



„ chord of posterior concavity (c N) 3'9 



Height of arc „ „ ' 1*25 



Ischium. 



Length of symphysis (a'p', fig. 6) 5"5 to 60 



Breadth along a line at right angles to symphysis to posterior edge 



of acetabulum (af F) 7'8 



Length from outer edge of its articulation with the pubis to its pos- 

 terior angle (b D) 10.1 



Length from anterior inner angle to posterior angle (ND) 7*725 



Minimum diameter across " neck " {rax) 24 



Length of symphysial margin for pubis (be) 2*4 



„ acetabular margin (b F) 2o 



„ chord of anterior concavity (cN) 3*85 



Height of arc of anterior concavity (x) 1*8 



