| 
WILLISTON! RANGE AND DISTRIBUTION OF THE MOSASAURS. 185 
perfect in the specimen, but appear not to have been denticulated. 
The surfaces are subdivided into narrow, slightly depressed planes, 
and the inner one is strongly striate at the base.” He is inclined 
to refer the tooth to A/osasaurus, a view in which Marsh coincides 
H 
after examination of the type.* 
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 referred to 
Holcodus, under the name ¢ympaniticus. The specimen which he 
described was from Mississippi. Later Cope applied the name 
Holcodus to two species from Kansas (//. con pheus and LT. tctericus), 
but which he later placed in P/atecarpus after the name Lestosaurus 
had been given to the genus represented by them. Cope in his 
Cretaceous Vertebrata (p. 141) 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 de- 
scribed, and the tail is not yet known. At one time, Cope stated 
that the tail vertebrae of Platecarpus had co-ossified chevrons, upon 
what authority I can not learn. Marsh based the distinction of 
Lestosaurus largely upon that character, apparently following Cope. 
The quadrate of P. éympaniticus, as figured by Cope certainly looks 
very much like that bone of the Kansas species, and the quadrate 
in this genus is a very characteristic bone. These questions then, 
are to be settled before the name Platecarpus can be finally ac- 
cepted for the Kansas forms: First, Is the typical Platecarpus 
identical with Mo/codus? 1 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 Platecarpus tympaniticus 
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. Tf 
the latter only is true, P/atecarpus 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 group within ‘the last 
twenty years. Perhaps we may expect more definite knowledge 
concerning them in the immediate future. There is no inherent 
improbability that the Alabama or Mississippi species are not con- 
generic with the western ones, inasmuch as we know positively that 
one genus at least, C/dastes, does occur in all these regions, and it 
does not seem at all unlikely that all of them are ccmmon to the 
different horizons. 
*Amor, Journ. Scl., June, 1872, 
