TEliTIAlJT VERTEBEATA OF THE FATtM. 
?.04 
owiii<>- to tlio STi Impression of the anterior and posterior faces respectively; in the 
anterior nenrals tlic antero-lateral borders arc much shorter than the postcro-lateral ones. 
'I'herc anm eijilit pairs of costals : as already mentioned, the first and last pairs meet 
in the middle line (text-fig. 97, A). The nuchal is large and wider than long; 
it is wider than the anterior vertebral plate which overlaps it ; the anterior border is 
emargiiiatc. There are eleven pairs of marginals, of which 4, 5, G, and 7 form the 
base of the bridge, and 5 and G unite with the mesoplastial [Ms.p.). The anterior 
free marginals have a I’onnded edge, the posterior ones arc somewhat expanded ami 
have a sharp edge. The axillary buttress is opposite the fourth marginal, the inguinal 
opposite tin; seventh : both buttresses are weaker and less developed than in most 
rienrodirans, tlie inguinal being the stronger of the two. 
The sn|)rapygal {I’ng.) occupies the summit of the posterior prominence above referred 
to ; it is roughly triangular in outline with convex sides and is of nearly the same 
shape as tlie oveilying vertebral shield. The pygal is notched in the middle line 
by the furrow separating the posterior pair of marginal shields. 
There are five vertebral shields (y.), the anterior of which is very narrow, being much 
narrower than the nuclial bone beneath it ; in Felomedusa and I’odocnemis the reverse is 
the case. The remaining vcrtebrals are roughly hexagonal in form, the antero-lateral 
borders being slightly shorter than the postero-latcral. The posteiior shield is very 
convex ; like the underlying suprapygal it is triangular in form, but is much larger 
(text-fig. 97, A, C). There are four costal shields and twelve marginals: no nuchal 
shield is present. On the anterior borders of the carapace the extent to which the 
marginals are exposed is very small, but posteriorly, where the carapace is somewhat 
expanded, the area is much greater. The relations of the shields to the underlying- 
bones are shown in the figure. 
'\'\\e plastron (text-fig. 97, B) is large ; its posterior free portion is wider than the 
anterior and is more than half as long again. The length of the bridge is about equal 
to the width of the front lobe, but much greater than its length. The anterior border 
is gently concave. The upper surface in this region is also gently concave from side 
to side, the concavity being bounded by thickened ridges borne on the cpiplastrals 
and anterior part of the hyoplastrals [Jhj.p.). From this ridge the surface slopes 
gently away to the lateral border of tlie anterior lobe. It a])pcars that the upper 
surface of the anterior lobe of the plastron was covered for some distance from its 
border by a scries of cpiplastral shields. 
The entoplastrou {Ent.) is a small escutchcon-sha])ed element, from the outer angles 
of which the sutures between the e])i])lastral and hyoplasfral bones run forwards, 
making an angle of about 45° with the long axis of the shell and terminating on the 
border of the plastron in the notch marking the end of the groove between the 
hnmeral and pectoral shields. '1 he suture hetwc'cn the hyo- and hypo])lastra (////./>., 
Eyp.p.) crosses at the level of the middle of the bridge and terminates externally 
