WEALDEN FORMATIONS. 13 



The vertebral centrums of the trunk show the shallow Amphicoelian character of 

 those of the Goniopholis and Teleosaurians. The smooth under or dermal surface of 

 part of the two median rows of the dorsal scutes are shown in the fore half of the 

 skeleton. In the hind half the upper or epidermal surface of the scutes is exposed, 

 showing in most the submedial longitudinal ridge. This is wanting in certain, probably- 

 lateral, scutes, of which a group is exposed at the fore part of the anterior portion of the 

 skeleton. One of these unridged, but toothed, scutes is figured at fig, 3, PI. IV. 



Of the limb-bones preserved may be recognised the right scapula (5i) and humerus 

 (53), the left humerus (53) with the radius (54) and ulna (55)^ followed by some dislocated 

 metacarpals and phalanges of the fore-foot. 



In the hind portion of the skeleton (fig. 2) the right femur (65), tibia (66), fibula (67), 

 with 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 PI. 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. Ill, had belonged ; but of the numerous evidences of 

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

 8, 14, 16, of PI. Ill : 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. 



^ Compare Tab. XI, ' Monograph on the Fossil Reptilia of the London Clay,' part ii, Crocodilia and 

 Op^z'rfta, Palseontographical volume, 4to, 1850. 

 " Quarto, tom. v, 2de partie. 



