384 Mr. A. S. Woodward on the 



the pleurocentrum appears as a very short bone tapering to 

 its pointed lower end. The hjpocentra are hu'i^er and more 

 massive ihan the pleurocentra. A typical example from the ab- 

 dominal region is shown of two thirds the natural size from the 

 anterior, interior, and lateral aspects in PI. XI. figs. 5, 5 «, 5 b. 

 The smooth saddle-shaped surface {not.) originally in contact 

 with the persistent notochord is again conspicuous, and the 

 great rugose surface on each branch of the bone resembles that 

 of the pleurocentrum which it meets. The stout lower portion 

 of the element is often a little distorted by crushing during 

 fossilization, but it always exhibits a pair of small rounded 

 depressions {x) in front and behind, as if they were facettes 

 for some relatively small intercalated parts which have disap- 

 peared. When viewed from below (fig. 5) a the hypocentrura 

 is seen to be flattened in the middle of tlic inferior face and 

 marked with a slit-like pair of longitudinal depressions, while 

 between this flattening and the transverse processes (tr.) the 

 surface of the bone exhibits a slight concavity. The processes, 

 seen also in side view (flg. 5 J, ^r.), are very short and stout, 

 and there is always a small irregular bony boss {ij) at their 

 baseantero-interiorly ; in the specimen figured they are placed 

 on the hinder half of the bone, the disposition of parts doubt- 

 less indicating that it belongs to the posterior abdominal 

 region. The end of the lateral branch of the hypocentrum is 

 rather truncated than pointed (fig. 5 b). Two detached hypo- 

 centra are exceptional in being much stouter in every way 

 than the others, and are remarkable as exhibiting a pair of 

 deep depressions in place of the usual transverse processes. 

 Comparison with the partially obscured example crushed 

 upon the back of the skull suggests that these belong to the 

 most anterior part of the vertebral column. 



Among the remains of vertebral arches the only satisfactory 

 specimens are some detached bases of the neural elements. One 

 of these, imperfect at its uj)[)er end, is shown of two thirds the 

 natural size from the anterior and externo-lateral aspects in 

 PI. XI. figs. 6, 6 rt, and the first figure is rendered more 

 instructive by an outline restoration of its fellow of the oppo- 

 site side. The specimen obviously belongs to the abdominal 

 region. The bone is comparatively massive at the proximal 

 end, and shows very clearly the facettes (c) for articulation 

 with two contiguous pleurocentra. It meets its fellow of the 

 opposite side in another considerable articulation {a) above 

 the neural canal (w.c), which is shown to have been re- 

 markably small, and there seems to have been even another 

 slight meeting below this canal. On the outer side of its 

 base the bone bears a prominent little boss {p-)j which, is 

 directed upwards and almost pointed. 



