METRIORHTNCHUS. 177 



backwards and a little upwards. The fused first, second, and third tarsals form a small 

 oval nodule of bone wedged in between the astragalus, the fused fourth and fifth 

 tarsals, and the upper ends of the first three metatarsals. The united fourth and fifth 

 tarsals form a larger nodule of bone, which unites proximally with the calcaneum and 

 distally supports the 3-4 metatarsals ; posteriorly it bears a short rounded prominence 

 (t.) which seems to have been thrust against the hinder face of the calcaneum. 



The first metatarsal {int. I.) is very wide at its proximal end, narrowing gradually 

 distally ; its anterior bolder is strongly convex, the posterior concave. At its proximal 

 end it terminates in an oblique border, bearing on its inner side a thickened convex 

 surface for union with the tarsus, while the outer side forms a strong angular 

 prominence ; distally this bone terminates in an oblique surface for union with the 

 first phalange, and is much more compressed than the second, third, and fourth 

 metatarsals. These increase in size in the order mentioned: at their upper end they 

 widen a little and terminate in convex surfaces for union with the tarsus ; when 

 articulated they are so arranged that, looked at from the dorsal surface, the posterior 

 face of the proximal expansion of each overlaps a little the metatarsal behind. The 

 shafts of these metatarsals are oval in section and they terminate distally in well- 

 developed convex surfaces for articulation with the phalanges. The fifth metatarsal 

 seems to have been always greatly reduced, and in the hind limb figured is represented 

 only by a small, triangular, claw-like plate of bone. The phalanges are more flattened 

 than the metatarsals and widen out considerably at their ends, some of the small 

 distal phalanges being hour-glass-shaped. One of the digits, probably the fourth, 

 terminated as a small flattened claw. 



In the large species (e. g. M. superciliosnm) the tarsus is not so well known ; it 

 differs from that of M. l&ve in having the constituent bones less flattened from above 

 downwards, and with more strongly convex articular surfaces. Otherwise the account 

 given above holds good for all the species so far as known. 



Seven species of Metriorhynclius from the Oxford Clay of Peterborough are 

 here recognised. Of these, three are new, three have been described in detail by 

 E. E. Deslongchamps in his ' Notes Paleontologiques,' and one by Lydekker, who 

 founded the genus Suchodus for the short-snouted form here called Metriorhynchus 

 durobrivense, there being no valid generic distinction between it and the other short- 

 snouted species of Metriorhynclius. 



The species here recognised may be distinguished by the characters given in the 

 following table : — 



A. Forms in which the surface o£ the cranial bone is without sculpture. 



1. Metriorhynclius Iceve. — A small species with a narrow skull ; teeth numerous, close-set, 



and small, upwards of 30 on each side of: the mandible. (Text-fig. 73, A.) 



2. Melriorhynchus leedsi. — Skull broader and more massive than in 1. Teeth large and 



closely set, about 36 in each maxilla. (Text-fig. 73, B.) 

 PART II. 2 A 



