172 DR. A. s. WOODWARD ON EXTINCT [Mar. 5, 



of the orbit, which is a Httle longer than deep and of about the same 

 size as the narial opening. The tympanic opening (au.) is almost 

 quadrilateral and equilateral, with rounded angles. It is scarcely 

 more than half as large as the orbit, and is specially remarkable as 

 being bounded behind by a gently convex, thick plate of bone, 

 which is as broad as deep. This bone is only preserved on the 

 right side of the fossil, but even here is too imperfect for the 

 determination of its constitution. It probably represents the 

 hinder part of the quadrate and squamosal fused with a dermal 

 bone. 



Viewed from below (Plate XVI.), the cranium proper is seen to 

 be a little broader than long, with the snout rounded, and a slight 

 constriction of the sides below the orbits. The palatal expansion 

 of the maxillse and premaxillee bears a large inner rounded ridge 

 (r.) concentric with the comparatively acute margin of the jaw, 

 thus indicating the herbivorous nature of the animal. The roof 

 of the mouth between this tritural border is raised into a dome 

 with the concavity downwards. The posterior nares {p.na.) thus 

 face backwards rather than downwards, and are separated by a 

 broad flattened bar, which seems to be formed by the premaxillse 

 in front and by the vomer behind. Immediately behind the 

 posterior nares, the antero -posteriorly arched area, which appears 

 to be an unusually large vomer, bears a sharp median longitudinal 

 keel. The limits between all the elements are uncertain, but the 

 palato-pterygoid region (pt.) of the palate is relatively very short 

 and broad, while the lateral margin of the pterygoid, though in- 

 complete on both sides, exhibits no trace of the curious rolled-up 

 lateral process so characteristic of existing Pleurodira. The 

 pterygoids clearly meet in the middle line, and there is a small, 

 transversely extended interpterygoid vacuity {i.pt.). The relatively 

 small basisphenoid (Jj.s.) is not quite in the same plane as the 

 basioccipital, but inclines a little upwards in front. Along narrow 

 buttress extends outwards from it on either side to the portion of 

 the quadrate bone which would bear the articulation for the 

 mandible ; but this region is too imperfect for precise interpretation. 

 The buttress is fused postero-superiorly with the otic bones {ot.), 

 which form a great mass at the sides of the occiput in which no 

 sutures are discernible. The basioccipital is concave on its lower 

 face ; and the occipital condjde, of uncertain constitution, is about 

 twice as broad as deep. The foramen magnum is slightly deeper 

 than broad, but comparatively small. The median crest of the 

 supraoccipital {s.occ.) is a slender lamina, somewhat expanded 

 above where it fuses ^ith the roof of the temporal fossae. Neither 

 this nor any of the otic bones extend backwards beyond the plane 

 of the occipital crest. 



The inner part of the cranium is well divested of matrix, and 

 two other interesting features are thus exposed. The hinder part 

 of the pterygoid is connected with the parietal region by a small 

 vertical lamina of boue on either side. The nasal cavity is com- 

 pletely separated from the orbit on each side by a thin bony 



