978 MR. W. p. PYOEAFT ON THE [Dec. 13, 



the 1st thoracic rib. There are altogether 6 of these articular 

 surfaces. 



The coracoid grooves are widely separated in the median line ; 

 the " dorsal lip " is represented by a slight projection near the 

 inner end, and the " ventral lip " by a somewhat more developed 

 process near the outer end, of the groove. The groove is slightly 

 curved, its convex surface being ventral, fairly wide, and deep. 



The posterior iatei-al processes are of great length in ApUnodytes 

 and Pygoscelis, longest in the latter, where they may exceed the 

 coracoid in length. They are slightly curved (outwardly), and 

 tend to meet in the middle line behind the metasternum through- 

 out the group. Only in Catarrhactes cJirysolophus and Eudyptula 

 minor are they so curved as to make the width across from the 

 process of one side to that of the other so great as to be equal to 

 {Eudyptula) or greater than {Catarrhactes) that across the anterior 

 lateral processes. The width of the posterior lateral processes 

 themselves varies slightly. From near the middle of each process 

 there arises a stroug ridge, which runs forwards to terminate in the 

 lateral border of the corpus sterni ; which, it should be remarked, is 

 bent, or reflected downwards to form a wide overhanging ledge 

 on each side of the sternum. Tlie metasternum is variable in 

 shape, being either pointed or rounded in form. 



The sternum remains as a single cartilaginous plate with a low 

 median keel till long after the coracoids and scapula have ossified. 

 In a half-grown A. forsteri in the Collection, the sternum is 

 represented by a pair of rhomboidal plates fused in the middle 

 line from before backwards to the posterior third, where they 

 remain widely separated. The keel is very feebly developed, and, 

 as in Steganopodes, is produced far forwards beyond the level of 

 the sternum, and tapers rapidly backwai-ds to disappear in the 

 neighbourhood of the sternal cleft just referred to. 



vi. The Pelvic Gikdle. (Fig. 1, p. 979.) 



The pelvis of the Impennes is not readily comparable with that 

 of any other group. Its most distinctive character is the great 

 backward lotatiou of the innominate bone. This is readily seen 

 if the pelvis is held so as to bring the synsacrum to the vertical. 

 A line drawn through the pre-ilium and pubis would describe an 

 angle of about 25°. Both external and internal borders of the 

 pre-ilium are greatly hollowed immediately in front of the aceta- 

 bulum. The ilio-ischiadic foramen never greatly exceeds the 

 acetabulum in size. The obturator foramen is never complete. The 

 pubis {pb.) never greatly exceeds the ischium (i's.)in length, is nearly 

 or quite straight, and runs parallel with the ischium, leaving a long 

 obturator fissure. Its free end never turns inwards. The ischium 

 is fused with the post-ilium, beyond which it projects slightly, and, 

 like the post-ilium, tapering to a point posteriorly forms a notched 

 posterior border. The post-ilium is expanded immediately over the 

 ilio-ischiadic foramen ; behind this it forms a sharp ridge projecting 

 considerably on either side above the level of the synsacrum. 



