ON SOME MESOZOIC FOSSILS. 5 
These pseudodonts, sheathed with horn, must have efficiently served 
a predatory tortoise in the capture of struggling victims. All traces 
of sutures have been lost from the surface of the specimen ; nothing 
therefore can be ascertained of the interrelations of the bones 
posterior to the post-frontal. Its reverse is largely covered with, 
broken bone, which probably formed part of the left side of the 
skull, but from these nothing is to be learned. 
The Adtjlt : Plate iv. — The rather sparse information supplied 
by the jounger cranium we may perhaps find supplemented to a note- 
worthy extent by those characters of the adult which have been demon- 
strated by atmospheric and manual operations. "When it came into 
my hands, weathering had already exposed the upper surface from 
the premaxillaries inclusive to the end, approximately, of the super- 
occipital spine; the parts thus made visible were the rostrum for 
the most part, the facial and anterior lateral regions, and the 
parietals as far back as the margins of the parietal vacuities 
appeared above the matrix. On the lower surface of the slab the 
contour of the lower jaw could be discerned through a thick 
coating of sediment. Development proved to be a tedious business 
owing to the toughness of the rock, an anxious one owing to the 
readiness of the soft bone to chip off in company with the firmly 
adhering matrix. It was interrupted by the slab proving itself 
unable to withstand continuous concussion by gradually falling apart 
in spite of clamping, and not resumed lest damage should be done 
to the exterior of the skull. The additional structures exposed are 
the post-frontal surface, the lower surface of the beak, the line of 
junction of the closed jaws, the tympanic antrum partially, the orbit 
partially, the mandible, and the palate sufficiently to show the 
position of the choanse. In form the skull approaches to that of 
an isosceles triangle, whose longer sides are somewhat, but distinctly, 
contracted at a point situated rather less than half their length 
from the apex — in other words, the convexity of the snout, 
continuous with that of the rest of the skull, so commonly seen in 
marine turtles, is here absent. The size of the fossil is a matter of 
some interest in relation to the type of the genus. Its dimensions 
are : — Total length to the apparent end of the spine, not less than 
195 mm.; greatest breadth across the parietals, 112 mm.; interorbital 
breadth, 60 mm. I perforce assume the correctness of Owen's 
estimate of the original length of his carapace, about 505 mm., and 
