Geological Society of London. 277 



plates which prolong the nasal passages ; vertebral centra mostly 

 procoelous ; coracoid elongated ; ala of the ilium very low in front, 

 its acetabular margin deeply notched; ischium elongated dorso- 

 ventrally, with its articular margin deeply excavated. — Genera : 

 Thoracosaurus, Holops, and recent forms. 



The Mesosuchia are intermediate in character between the other 

 two groups ; the Parasuchia, where they differ from the Mesosuchia, 

 approach the Ornithoscelida and Lacertilia, especially such as Hat- 

 teria and Hyper oclapedon, with amphicoelous vertebral centra. The 

 Eusuchia, on the other hand, are the Crocodilia which depart most 

 widely from the Ornithoscelida and Lacertilia, and are the most 

 Crocodilian of Crocodiles. 



After indicating at some length the succession of modifications in 

 the above three groups, the author remarked that if there is any 

 solid ground for the doctrine of evolution, the Eusuchia ought to be 

 developed from the Mesosuchia, and these from the Parasuchia, and 

 showed that geological evidence proved that the three groups made 

 their appearance in order of time, in accordance with this view. 

 Thus in the Trias there are the genera Belodon and Stagonolepis of 

 the sub-order Parasuchia. In the Upper Lias we have Steneosaurus, 

 (Ifystriosaurus) and Pelagosaurus, the first represented also in all 

 Mesozoic formations up to the Kimmeridge Clay ; in the Fuller's 

 Earth Teleosaurus and Teleidosaurus occur ; in the Kelloway Rock 

 Metriorhynchus, also met with in the Oxford Clay and Kimmeridge 

 Clay ; in the Wealden, Goniopholis, Macrorhynchus, Pholidosaurus, 

 and unnamed Teleosaurians ; and in the Upper Chalk Hyposaurus ; 

 all belonging to the Mesosuchia. In the Upper Chalk again the 

 Eusuchia make their appearance, represented by the genera Thora- 

 cosaurus, Holops, and Gavialis (?). How far back the Parasuchia 

 extend in time is not known, but they are not found in any forma- 

 tion subsequent to the Upper Trias. The author described a frag- 

 ment of a skull of a Wealden Crocodile, in which the posterior nares 

 are smaller and situated further back, than in Metriorhynchus or 

 Steneosaurus. 



Of the nearest allies of the Crocodilia, the Lacertilia and Orni- 

 thoscelida, the former may be traced back from the present day to 

 the Permian epoch, and the latter from the later Cretaceous to the 

 Triassic epoch. The author discussed the question whether these 

 types exhibit any evidence of a similar form of evolution to that of 

 the Crocodilia. The cranial structure of the Permian Lacertilia is 

 almost unknown, and the only important deviation from the type of 

 the existing Lacertilia in the skeleton is that their vertebrae are 

 amphicoelous, not procoelous. With this exception there is no evi- 

 dence that the Lacertilian type of structure has undergone any 

 important change from the later Palaeozoic times to the present day ; 

 and this change seems to have occurred earlier in the Lacertilia than 

 in the Crocodiles, as a sacral vertebra of a Lizard from the Purbecks 

 has the centrum concave in front and convex behind. 



With regard to the Ornithoscelida, the author noticed that the 

 researches of American Palaeontologists proved the existence of 



