290 
TEKTIARY A^EilTEiniATA OF THE FAYUM. 
short anterior and a long posterior side. The sixth is pentagonal and is wedged in 
between tlic front of the sixth costal plates, which behind it meet in the middle 
line, as also do the seventh and eighth costals. Of the eight pairs of costal hones 
the tirst is much the largest. The marginals are badly preserved, hut there seem 
to have been ten or eleven pairs : the last marginals and the pygals are somewhat 
enlarged, giving the carapace its peculiar caudate appearance ; though it is possible that 
this may be partly due to crushing, which has bent the posterior end of the shell a little 
upwards. The suprapygal is roughly triangular in outline, the sides being convex. The 
surfaces for the attachment of the ilia and scapulae are exactly as in F. madrtr/ascariensis ; 
and the buttresses are similar in position and quite as strongly developed as in that 
species, thus differing from the comparatively slightly developed buttresses of Stereogewjs. 
Text-fig. 92. 
Carapace and plastron of Podocnemis antirpia : A, carapace ; B, plastron. 
Enl., entoplastral l)one ; Ep., epiplastral bone; JPj p., byoplastral bone ; llijp.p., bypoplastral bone; 
Ms.p., inesoplastral bone ; Nu., nuchal bone ; Xi.p., xipbiplastral bone. About A nat. size. 
(From the Ann. & Mag. Nat. Hist. [7J vol. xi.) 
In the plastron (text-fig. 92, B) the entoplastral bone {Ent.) is rhomboidal in 
form : from its outer angles the sutures between the epi- {Ej^).) and hyoplastrals {llg.p.) 
run outwards and backwards for a short distance and then turn forwards, at least on 
the inner surface ; on the outer face the sutures are obscure and, owing to the varying 
degrees of overlapping of the adjacent bones, may have been rather different from those 
on the inner face. The straight suture between the hyo- and bypoplastral {Ugp-P-) 
crosses about the middle of the bridge and terminates in the outer angle of a small 
lateral inesoplastral {Ms.p.). The xiphiplastra [Xi.p.) terminate in points, the whoh- 
posterior border being deeply notched, 'i'he bases of the fused pubes and ischium 
