MR. J. W. HULKE ON THE POLACANTHUS EOXII. 
657 
looks singularly short and slender. Its cross-section at the middle is roughly trigonal, 
and the diameters here are 4'5 centims. and 5'5 centims. Owing to the twist of the 
shaft, that which below is the inner border becomes as it ascends the broad anterior 
surface above; and the narrow surface at the upper end lying between the outer 
condyle and the prgecnemial crest as it descends becomes towards the distal end the 
broad antero-external surface. 
Of the fibula only a small fragment attached to the outer border of the antero- 
external surface near the lower end now remains. 
Foot .—The only parts of this which can with certainty be identified are two 
metatarsals (Plate 72, fig. 8). In the great size of their joints and shortness and 
slenderness of the shaft they repeat the most striking features of the femur and tibia. 
Their distal end has the usual pulley form. The condyles project strongly towards 
the sole, and the pits for the attachment of the lateral ligaments are large and deep. 
The proximal end is most expanded vertically. The length of the best preserved meta¬ 
tarsal bone is about 8’5 centims., the breadth of its distal end is 4'5 centims., the 
longer diameter of its proximal end about 7'5 centims., and the diameter of the middle 
of the shaft nearly 2 centims. 
Respecting the bones considered unguals by Mr. Fox I cannot speak confidently. 
Their form is broad, depressed, and blunt. 
Dermal armour .—Together with the endoskeletal bones a highly developed dermal 
armour was found. Mr. Fox told me that when he first laid this bare it formed so 
continuous a mail that his first impression was that he had exposed the carapace of a 
huge turtle. It measured 3 feet by 3 feet 3 inches, covered the loins, and it was 
thinner at its middle near the vertebral column than towards its borders. It is now 
I fear irreparably damaged and beyond reconstruction. Broken up into countless 
pieces through hasty and incautious removal from the cliffs, these have in 15 years 
cracked and fallen into numberless smaller fragments; the attempt to rejoin which 
would be a hopeless undertaking. 
Scutes of three forms are readily distinguished : a, simple flat scutes; /3, keeled 
scutes; and y, spined scutes. Those of the first kind are most numerous. Since 
none are now entire their shape and dimensions can only be approximately ascertained. 
They varied greatly in different situations, since some were certainly more than 
26 centims. across, whilst the breadth of others did not exceed 1 centim. Their 
thickness ranges between 3 centims. and 5 centims. Their deep or inner surface is 
smooth and their outer surface is studded with scattered tubercles. (Plate 71, fig. 3.) 
A smaller number of scutes are keeled. The keel, in some, itself unsculptured, rises 
within a circle of one or more rows of tubercles which are separated from the margin of 
the scute by a sunken groove, the inner lip of which is thin and projects. (Plate 70, 
figs. 3, 4, and Plate 72, fig. 4.) It is probable that into this groove fitted the thin 
edge of the adjoining scute, a mode of articulation giving flexibility with security 
against dislocation. The deep surface of these scutes is smooth and sinuous. A few 
MDCCCLXXXI. 4 Q 
