. 141 



and its deep emargination in front, where- well developed. From its general 

 characters, I anticipate that the quadrate bone of this species will prove to 

 be more like that of the Platecarpi ; that of G. planifrons is that of the genus 

 to which I have referred it. 



PLATECAKPUS, Cope. 



Vertebree very numerous; caudal series very elongate; zygapophyses 

 strong; zygosphen wanting, or very radimental. .Chevron-bones free. Teeth 

 subround in section, acute, and curved. Humerus short and wide. 



While the form of the humerus in this genus is that of Clidastes, the 

 vertebral articulations are those of Liodon, the zygapophyses being, however, 

 stronger. The teeth are different from either. 



Besides the characters assigned to this genus in the analytic table 

 already given, Platecarpus is characterized by the position of the fronto- 

 parietal fontanelle on, or very close to, the coronal suture, instead of in the 

 broad plate of the parietal bone posterior to the suture, as in Clidastes. The 

 genus is also characterized by the form of its teeth, which are neither com- 

 pressed, as in Liodon, nor broadly, angularly faceted, as in Mosasaurus (and 

 Holcodus, fide Marsh), but are curved and subcircular in section. The 

 exposure of the roots of the palatine teeth is largely less, or scarcely greater, 

 on the outer than on the inner side. The form of the cranium is, in this 

 genus, less elongate than in Clidastes, and the muzzle is often quite short 

 and obtuse. The caudal vertebrae of the type-species P. tympaniticus are 

 unknown; but its quadrate bone and the forms of its cervical vertebrae and 

 palatine teeth are quite similar to those of the other species here referred to 

 Platecarpus. Professor Marsh has referred the same species to a genus, 

 Lestosaurus, Marsh, of which the species L. si?nus, Marsh, is regarded as type, 

 and which he regards as nearly coextensive with the genus I previously 

 defined under Dr. Gibbes's name Holcodus. He finds the coracoid of L. simus 

 to be deeply incised, as is often the case in Lacertilia. 



The name which I formerly used for this genus was originally applied 

 by Dr. Gibbes, 1 of Charleston, to a species represented by teeth from the 

 Cretaceous of Alabama, but of which no other portions were known. The 

 teeth of the Kansas species referred to it are somewhat similar in character 

 to those described by Gibbes ; but it is evident that the latter belonged to an 



' Oil Mosasaurus ami allies, in Smithsonian Contributions to Kiisuvledgw, 1851, il : plates. 



