430 PROF. T. H. HUXLEY ON STAGONOLEPIS ROBERTSONI, 



PARASUCHIA. 

 Trias. Belodon, Stagonolepis. , 



, MESOSUCHTA, 

 Lower Lias. 



Upper Lias. Steneosaiirus, (Mystriosaurus), Pelagosaurus. 

 Inferior Oolite. * 



Puller's Earth. * Teleosaums, Teleidosaiirus . 

 Great Oolite. * 

 Kelloway Rock. * 



Metriorhynchus. 

 Oxford Clay. * * 



Coral Rag. * 



KlMMERIDGE CLAY. * * 



Portland Oolite. 



"Wealden. Goniopholis, Macro ryhnehiis, Pholidosaurus, 



and unnamed Teleosaurians. 

 Lower Greens and. 

 Gatjlt. 



Upper Greens and. 

 Lower Chalk. 

 Upper Chalk. Hyposaurus. 



EUSUCHIA. 

 Thoracosaurus, Holops, Gavkdis (?). 



This table shows that the order in which the three divisions of 

 the Crocodilia make their appearance is the same as the order of 

 their departure from the Lacertilian, and approach to the highly 

 specialized Crocodilian, type. 



How far back the range of the Parasuchia extends we have no 

 means of judging. Nothing is known of them, at present, subse- 

 quently to the Upper Trias. Of the two known genera, Stagono- 

 lepis would seem to approach the Mesosuchia somewhat more closely 

 than Belodon does, but it is far on the Parasuchian side of the 

 boundary line between the two suborders. There is a hiatus in our 

 knowledge of the Crocodilia answering to the Lower Lias, from 

 which, up to this time, no Crocodilian remains are certainly known. 

 With the Upper Lias our acquaintance with the Mesosuchia com- 

 mences ; and they are represented, without interruption, as far as the 

 "Wealden inclusively. Then follows a great break, answering to the 

 Greensands, Gault, and Lower Chalk, during which period there is 

 no evidence as to the characters of the Crocodilia. 



It is at the end of this unrepresented interval that the Eusuchia 

 make their appearance, under forms exceedingly similar to the 

 existing long-snouted Crocodiles. Nevertheless the Mesosuchia 

 persisted until the end of the Cretaceous epoch. The ranges of the 

 Eusuchia and the Mesosuchia therefore overlap in the later Cre- 

 taceous epoch, where the Eusuchia are represented in the Greensands 



