Williston.] Mosasaurs. 179 



at the base." He is inclined to refer the tooth to Mosasaurus, 

 a view in which Marsh coincides after examination of the type. 57 

 I cannot agree with these authors. Whatever the tooth may- 

 be, it is not that of a Mosasaurus. Professor Cope erected the 

 genus Platecarpus for a species which Leidy had previously re- 

 ferred to Holcodus, under the name tympaniticus. The specimen 

 which he described was from Mississippi. Later Cope applied 

 the name Holcodus to two species from Kansas (H. coryphaeus and 

 H. ictericus) , but which he later placed in Platecarpus, after the 

 name Lestosaurus had been given to the genus represented by 

 them. In his Cretaceous Yertebrata (p. 141) he says: "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 a different animal more nearly allied to 

 the true Mosasaurus." Of Platecarpus tympaniticus very little of 

 the skeleton has been described, and the tail is not yet known. 

 At one time (Ext. Batr., etc.) Cope stated that the tail verte- 

 bra' of Platecarpus had coossified chevrons, upon what authority 

 I cannot learn. Marsh based the distinction of Lestosaurus 

 largely upon that character, apparently following Cope. The 

 quadrate of P. tympaniticus, as figured by Cope, certainly looks 

 very much like that bone of the Kansas species, and the quad- 

 rate in this genus is a very characteristic bone. These questions 

 then, are to be settled before the name Platecarpus can be finally 

 accepted for the Kansas forms : First, is the typical Platecarpus 

 identical with the Holcodus f I believe that it is. The teeth of 

 the Kansas forms agree perfectly with Leidy 's description and 

 figure of the type specimen of Holcodus. Second, is P. tympan- 

 iticus congeneric with the Kansas species placed in this genus? 

 This also appears to be true, but it is by no means yet proven. 

 If both propositions are true, our species must be known as 

 Holcodus. If the latter only is true, Platecarpus will be retained ; 

 while if the former is alone true, the name Lestosaurus will take 

 precedence. It is a pity that little or nothing has been added 

 to our knowledge of the southern and eastern species of this 



57. American Jour. Sci., June, 1872. 

 14— [V 



