Range and Distribution of the Mosasaurs, 
With Remarks on Synonymy. 
BY 3S.) We. - WILLISTON. 
With’ Plate 2X, 
The Mosasaurs are at present known from four remote regions of 
the world—-North and South America, Europe and New Zealand. 
Doubtless they lived over the greater part of the earth and may be 
expected to be found wherever the deposits in which they occur are 
found. Their geological range is confined exclusively to the Upper 
Cretaceous, from the time corresponding to the upper part of the 
Dakota to that of the lower part of the Laramie, or from Upper 
Cenomanian to the Lower Danian. The correlation of the Ameri- 
can Cretaceous deposits with those of Europe, or even with each 
other is by no means exact, or even approximately exact. Never- 
theless the equivalency of the different strata and epochs is sufh- 
ciently well determined to admit of approximate pesults, anduit iis 
one of the purposes of this paper to bring what evidence the 
Mosasaurs—-typical Cretaceous reptiles—may present, bearing upon 
the subject. 
The oldest Mosasaurs are apparently those described by Hector 
from New Zealand, which he referred to the genera Liodon and 
Taniwhasaurus Hector.* Thegenus Lzodon Owen, Dollo has recently 
shown to be a synonym of Mosasaurus. |. Whether or not Hector’s 
species is congeneric with those placed under Lvodon by Cope is not 
certain, though it is evident that it is closely allied.  Zamwhasaurus 
is as clearly of the Platecarpus type, and may possibly belong to 
that genus. 
The most recent form is the historical Aosasaurus giganteus 
Soemmering (7. Camperi, WM. Hoffmani) from the Mestricht beds 
in the Lower Danian. These three forms, 7)/osaurus, Platecarpus 
and Mosasaurus represent three distinct and divergent types, which 
I will call the Tylosaurina, Platecarpinz, and Mosasaurine, cor- 
*On the Fossil Reptilia of New Zealand, Trans and Proc., New Zoaland Institute, 
Vi. 888, 1873. 
+Bull. Soc. Belg. Geol., vii, 79. 1892. 
7%) KAN. UNIV. QUAR.. VOL. VI, NO. 4, OCT., 1897, SERIES A. 
