AMERICAN AMPHICCELIAN CROCODILES 13 



In conclusion, from the study of considerable material, and the 

 attentive perusal and consideration of the facts and arguments 

 offered, especially by Koken,' I share the opinion of most recent 

 writers on the crocodilia that the separation of the amphicoelian 

 and procoelian crocodiles by Huxley, which at one time seemed so 

 brilliant a generalization, into the suborders Mesosuchia and 

 Eusuchia is unnatural and artificial. I believe that the change 

 from, amphicoelous to procoelous vertebrse has been concurrent in 

 two, possibly in 

 all three, of the 

 modern types of 



Crocodilia, the % 



Gavialidas, Tom- - ) ,1' 



istomidcc, and '-0* 



Crocodilidae. .-' ;/ 



In the specimens 

 from the Hailey 

 shales the centra 

 may best be de- 

 scribed as ccel- 

 oplatyan, the an- 

 terior concavity 



y^ ^ Fig. 3. — Coelosuchiis rcedii. Proximal extremity 



tenor one Snai- of right humerus, one-half natural size. 



low, if any. The 



change from this form to a distinctly procoelous one is not at all 

 difficult to un:1erstand, and was brought about, I beheve, by the 

 same or similar causes in the different phyla. The true teleosaurs 

 could not have been ancestral to any of the modern crocodiles, since 

 the marked difference in the size of the fore and hind limbs was a 

 specialization for aquatic habits, as was carried to a greater degree 

 in the Thalattosuchia,^ and could not have reverted to the more 

 modern amphibious type, even that of the gavials. That the true 

 crocodiles began existence as terrestrial, or at least terrestro-amphib- 



1 Koken, Paleontologische Ahhandlungen (1S87), Vol. Ill, p. 105; Zeitschrijt der 

 Deiitschen geologischen GeseUschajl, 1888, p. 767. 



2 Fraas, Paleontographica, Vol. XLIX (1902), p. i. 



