PROREPTILIA 287 



Cricotus, with several species in Texas and Illinois. C. hetero- 

 clitiis was perhaps 10 feet long and probably aquatic. The 

 skull has a long, narrow, depressed snout, the margins over- 

 hanging those of the lower jaw ; its surface is encased in dermal 

 bones, most of which still show sutures, so that for instance 

 postfrontals, postorbitals, supratemporals and squamosals can be 

 distinguished ; all these are in contact with the long parietals 

 and with the quadrato-jugal arch, covering the temporal region ; 

 but the supratemporals have a free projecting border, like the 

 squamosals of the crocodiles. According to Cope's description 

 the basioccipital is connected with the first vertebra by an 

 undivided discoid " intercentrum," probably the true centrum, while 

 the first basiventral mass, which would be, if independent, the 

 first true intercentrum, is more probably connected with the first 

 neural arch, thus constituting the ring of the atlas. 



The vertebrae are still temnospondylous, but no longer 

 tripartite. The neural arch is fused with the interventralia into 

 one mass, which carries the capitula and tubercula of the ribs, 

 while the united basiventrals still remain as separate intercentral 

 wedges. In the tail these wedges carry chevron-bones, and are 

 enlarged into thick almost complete discs, or rather rings, while 

 the whole vertebral column is still perforated, as also in Eryops, 

 by the chorda dorsalis. The tail is long. The digits are devoid 

 of claws. 



Eemains of dermal armour exist on the throat in the shape 

 of several large gular plates, while the whole belly is covered 

 with many closely packed bony scales, which are arranged in 

 chevron-shaped transverse rows. 



Probably several other genera of American Permian and also 

 of European Permian strata will, when better known and criti- 

 cally examined, have to be referred to the Proreptilia. Thus for 

 instance the European Ifelosmirus may have aiSnities with 

 Eryops, while Bijjlovertebron of Bohemia seems to be allied to 

 Cricotus. The difficulty of division will lie with those Lower 

 Permian Amphibia which, like Archegosaurus, Euchirosaurus, 

 Actinodon, possess tripartite vertebrae, which at first sight are 

 strikingly like those of Eryops. But the tail-vertebrae permit 

 of no mistake, and since these are quadripartite in Archegosaurus, 

 Chelydosaurus, and Sphenosaurus, these genera are safely to be 

 classed with the Amphibia, unless, indeed, for mere argument's 



