500 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.38. 



The chief generic distinctioD was found in the contribution of the 

 splenial to the symphysis which was equal to one-fifth of the hitter's 

 length. 



L< idyosuchus canadensis Lambe is the type-species of the genus. 



The characters displayed by the specimens considered in the pre- 

 ceding pages, combined with those shown by the Judith River species, 

 show that the genus Leidyosuchus may now be characterized as 

 follows: Generic characters. — Cranium short and of moderate breadth; 

 /in hitd/ aspect of the premaxillce slightly lengthened, with posterior 

 borders convex and indented medially by the anterior processes of the 

 ma.ri/ht . Nasals not ( ?) reaching nares. Frontal s contributing /<> 

 boundary of supratemporal fossa. Premaxillary fissure and external 

 nares both heart-shaped. Posterior nares wholly inclosed by pterygoids 

 and placed about their middle. Mandibular symphysis short and 

 contributed to by the splenial. Upper teeth more numerous than lower; 

 first lower received into a pit and third and fourth into a notch in the 

 cranium; third lower quite as large as fourth. 1 '< rtebra procoelian. A 

 dorsal and ventral armour. 



Discussion. — A study of the specimens considered in the preceding 

 pages confirms the conclusions of Lambe, that Leidyosuchus repre- 

 sents a procoelian, brevirostrate form of Eusuchja. 



A review of the characters of the skull shows thai they combine 

 those which have been attributed to the genus Crocodilus and the 

 genus Alligator. The resemblances to the latter may be seen in the 

 reception of the anterior teeth of the lower jaw in pits which do not 

 perforate the dorsal surface of the premaxilhe; in the relative size 

 and everted position of the orbits; and in apparently having the 

 smaller lower teeth biting within the upper teeth. On the whole, 

 however, the characters displayed by the known specimens of 

 Leidyosuchus places that genus nearer to the crocodiles than other- 

 wise. 



Lambe has already called attention to the resemblance of the den- 

 tition to th.it of Diplocynodon, and the discovery and study of more 

 complete material than that to which he had access show other 

 resemblances. The. more important likenesses are the participation 

 of the frontal in the boundary of the supratemporal fossa; and the 

 exclusion (?) of the nasals from the anterior narial opening. 



The intermediate position of the posterior, nares La one of the inter- 

 est ing features of this genus, and entirely in accord with its geological 

 position. For instance, in the Triassic Belodon the posterior nares 

 open in front of both palatines and pterygoids. In the Jurassic 

 Teleosaurus the posterior nares are farther back and surrounded by 

 the palatines. In the Cretaceous Leidyosuchus they lie still farther 

 back, in the middle of the pterygoids. Finally, in the Tertiary forms 

 the arrangement is approximately as found in living crocodiles. 



