PURBECK CROCODILES. 653 



metacarpals and phalanges of the fore-foot. In the hind portion of the skeleton (fig. 2) 

 the right femur (fjs), tibia (66), fibula (e;), vvith the four metatarsals and scattered 

 phalanges, are preserved. 



All the limb-bones show the ordinal Crocodilian characters, but the proportion of 

 the fore to the hind limb is that of the Procoelian division, not that of the Teleosaurs.^ 

 In this respect, as in the proportions of the maxillary bones and teeth, the advance to 

 Tertiary types of Crocodilia is manifested. As in these the Theriosuchus was better 

 adapted for locomotion on dry land than were the Teleosaurs. 



In Theriosuchus the breadth and shortness of the antorbital part of the skull in 

 proportion to the part behind exceeds that in any modern broad-snouted Crocodile. 

 Even in the young ' Crocodile a deux arretes,' figured in PL I of Cuvier's ' Ossemens 

 Fossiles,'^ a transverse line across the fore part of the orbits equally bisects the skull, 

 omitting the mandible. In Theriosuchus the same line leaves in advance six thirteenth 

 parts of the length of the skull. 



This proportion suggested at first view the immature state of the individual to 

 which the subject of fig. 3, PI. 44, had belonged; but of the numerous evidences of 

 Theriosuchus pusillus none were larger than those figured in PI. 45, and in figs. 3, 4, 

 8, 14, 16, of PI. 44 : several other fragmentary evidences had come from smaller 

 individuals. 



I conclude, therefore, that, as in the case of most species notable for their diminutive 

 size, immature characters of the larger species of the genus are associated with such 

 dwarfishness of the adults. The only known mammals of the Purbeck period charac- 

 teristic, moreover, like the dwarf Crocodiles, of the fresh-water ' Feather-bed ' deposits, 

 are of diminutive size, and the carnivorous Saurians seem to have been thus adapted in 

 dimensions and force to their prey. 



I estimate the average length of a mature Theriosuchus at 18 inches. The length of 

 the skull, taken as that of the mandible, is 3 inches 6 lines. In the articulated skeleton 

 of a modern Crocodile the angle of the lower jaw extends to the third cervical vertebra. 

 In Alligator lucius the trunk from the third cervical to the last sacral vertebra inclusive 

 is nearly equal to two lengths of the skull ; the length of the tail is 2^ lengths of the 

 skull. The trunk oi Theriosuchus so defined includes two lengths of the skull. The 

 tail, as indicated by fig. 2, PI. 45, equalled 2^ lengths of the skull. 



In the long-jawed Gavials and Teleosaurs the trunk includes about 1| length of 

 the skull ; but the tail is proportionally longer than in the short- and thick-jawed 

 Crocodiles. 



^ Crocodilia, PI. 11. 



2 Quarto, torn, v, 2de partie. 



