116 MARINE REPTILES OF THE OXFORD CLAY. 



is produced backwards into two pointed processes separated by a concave surface ; 

 tbe postaxial process is the more prominent. 



The first metatarsal (I, text-fig. 47) is much the stoutest ; it is much expanded and 

 thickened at its upper end, where it bears a large articular surface for the astragalus, 

 concave externally and convex internally. The shaft is compressed and strongly curved 

 outwards ; at its upper end, on the outer border, there is a slight rugose prominence ; 

 distally it narrows and terminates in an obliquely grooved articular surface for the first 

 phalange. The remaining metatarsals are straight and more slender, the third being 

 the largest ; at their proximal ends they bear a somewhat convex articular head, from 

 which a small flange projects outwards and overlaps the front of the upper end of the 

 next metatarsal. Distally, the second metatarsal bears a grooved articular surface for 

 the phalange, but in the third and fourth the distal articulation is simply convex from 

 above downwards ; the sides immediately above the distal articular surface are concave, 

 at least in the second and third. The fifth metatarsal seems to be represented by the 

 small irregularly shaped bone shown in text-fig. 47 A, V %. 



The exact arrangement of the phalanges is not known. The stoutest of those 

 preserved probably belong to the first digit, which no doubt terminated in a 

 well-developed ungual phalange, some specimens of which are preserved. At its 

 proximal end the ungual phalange bears a deeply concave articular surface. The dorsal 

 sui face is strongly convex from side to side, the ventral face only slightly so. Distally, 

 the bone is compressed from above and is much roughened, having evidently been 

 covered with a horny nail in life. Whether the terminal phalanges of the other digits 

 were similar is not known ; probably they were not, since not more than one such claw 

 has been found with any foot. 



Dermal Armour (PI. V. figs. 6-10; PI. VI. figs. 4, 5; PI. VII. fig. 6; 

 text-figs. 48, 49). — The dermal armour consists of a great number of bony scutes 

 varying much in shape and size, according to the regions of the body in which they 

 occur. Unfortunately, the scutes are always found scattered, so that their exact 

 arrangement cannot be determined. Probably it was much as in the allied Mystrio- 

 saurus, in which there is a pair of rows of scutes meeting, or nearly meeting, in the 

 middle dorsal line, probably a lateral row on each side of the tail, and a ventral 

 plastron, the arrangement of the scutes in which is not certain. 



In Steneosaurus the scutes, presumably from the dorsal region (text-fig. 48, A), are 

 roughly quadrate in outline, their outer surface bearing a sculpture of deep pits, the form 

 and arrangement of which vary in the different species, while the inner surface is smooth. 

 The inner (median) edge of the scute is straight and united in suture, or at least was 

 in contact with its fellow of the opposite side. The outer edge is convex. There is a 

 longitudinal ridge considerably nearer the outer than the inner border of the scute, and 

 terminating anteriorly in a tooth-like peg fitting under the- posterior border of the 

 scute in front, which also overlaps the smooth bevelled anterior border of its successor. 



