290 



TEETIAEY VEETEBEATA OF THE FATtfM. 



short anterior and a long posterior side. The sixth is pentagonal and is wedged in 

 between the 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 bones 

 the first is much the largest. The marginals are badly preserved, but 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 P. madagascariensis ; 

 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 Stereogenys. 



Text-fig. 92. 



i not.sije. 

 Carapace and plastron of Podoenemis antiqua : A, carapace ; B, plastron. 

 Ent, entoplastral bone ; Ep., epiplastral bone ; Hy.ji., hyoplastral bone ; Hyp.p., bypoplastral bone ; 

 Ms.p., mesoplastral bone ; Nu., nuchal bone ; Zi.j?., xiphiplastral bone. About ^ nat. size. 

 (From the Ann. & Mag. Nat. Hist. [7] vol. xi.) 



In the plastron (text-fig. 92, B) the entoplastral bone (E^it.) is rhomboidal in 

 form : from its outer angles the sutures between the epi- {Ej>.) and hyoplastrals (Hi/.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 {Hyp.f.) 

 crosses about the middle of the bridge and terminates in the outer angle of a small 

 lateral mesoplastral {Ms.p.). The xiphiplastra {Xi.p.) terminate in points, the whole 

 posterior border being deeply notched. The bases of the fused pubes and ischium 



