Two new Species of Fossil Tortoises. 147 



where the sulci marking^ their boundaries are well defined. 

 The whole shell was very massive, some of the plastral plates 

 measuring upwards of 13 mm. in thickness. 



The arrangement of the plates will be best understood from 

 the figures. There seems to have been a pygal of peculiar 

 form, narrowing towards the margin of the shell (fig. 1, B) : 

 it is represented in part by its impression only, but the 

 sutures can be followed. The lower supra-pygal is a small 

 well-defined bone, crescentic in outline, with the concavity 

 downwards. The nature of the bone above is doubtful, the 

 sutures in this region being obscure and cracks numerous : 

 it may be a second sypra-pygal or the posterior pair of 

 costals unitingiin the middle line. If this last interpretation 

 is correct, the animal possessed at least nine pairs of costals — 

 a quite exceptional condition. The marginals were very 

 massively constructed : all preserved are much broken at the 

 edges. The plastron (fig. 1, A) is chiefly remarkable for the 

 presence of two mesoplastrals on the left side, while there is 

 only one on the right. This reduplication of the plastral 

 element is interesting, because it may indicate a tendency to 

 revert to an earlier condition in which the number of paired 

 elements in the plastron was greater than in later forms. The 

 posterior lobe narrows gradually backwards from the bridge, 

 and its posterior end is slightly notched. The anterior lobe 

 is broadly rounded ; the form of the epiplastrals cannot be 

 clearly determined, but it can be seen that their upper border 

 was tlnckened, rounded, and covered with the characteristic 

 sculpture. The entoplastron is incomplete, but was probably 

 lozenge-shaped. The hyoplastra are incomplete in front. 

 The single mesoplastron on the right side is very wide, 

 almost as wide as the two occurring on the other side taken 

 together. On both sides the raesoplastra widen out towards 

 the bridge, this being particularly marked in the anterior 

 one on the left side. The form of the hypo- and xiphiplastra 

 present no special peculiarities. The grooves marking the 

 outline of the horny scutes are well marked on the plastral 

 surface, but coidd not be seen on what remains of the 

 carapace. The boundary between the humeral and pectoral 

 scutes crosses just l)ehind the posterior angle of the ento- 

 plastron, tliat between the pectorals and abdominals is on the 

 mesoplastra. The grooves between the femoral and anal 

 scutes slope strongly backwards, and arc confined to the 

 xiphiplastra. On the bridge there were three or four sub- 

 marginal scutes. The ])resence of the horny scutes on a 

 shell in which the sculpture is so strongly developed seems 

 remarkable. 



