180 KANSAS UNIVERSITY QUARTERLY. 
The rudimentary or possibly functional zygosphene among the 
Platecarpine, or some members of it and the complete zygos- 
phene in Cédastes; together with the shortened muzzle and 
more fully ossified paddles, indicates a much closer relationship 
between the Platecarpinae and Mosasaurine than between either 
and the Tylosaurine.-: In the last we find, in some forms at least, 
that the fifth finger is actually longer than the fourth, with as 
many: phalanges, and that the carpus and tarsus are almost 
wholly unossified. If we assume with Dollo that the zygos- 
phene is a primitive, character, and it must be unless it had an 
independent origin among the Mosasaurs, then C7@dastes would 
be the most generalized and 7\/osaurus the most specialized 
of the Mosasaurs. In the paddles and skull, 7/osaurus is with 
hardly a doubt, more specialized than anyother genus. However, 
although C/das/es may retain some of its primitive characters, 1t 
certainly shows in many other respects a high degree of specializa- 
tion, 
In the accompanying plate are shown the side views of skulls of 
two of these types, the Tylosaurine and Platecarpine. The third 
type, the Mosasaurina, may be seen by reference to plate XV, in 
Vol. Ill, of this OuarTERLY. 
[ give below a tabular review of the known genera of the Mos- 
asaurina arranged in systematic sequence, using the European 
time-epochs for comparison’s sake. Of course it is understood that 
the exact equivalency of these time-periods is yet a matter of un- 
certainty. 
TYLOSAURINA. 
Hind feet functionally pentadactylate. Trunk short, the tail 
proportionally long, not dilated distaliy. Tarsus and carpus 
almost wholly unossified, the phalanges numerous. Vertebra 
wholly without zygosphene.. Premaxillary projecting into a long 
rostrum in front of the teeth. Quadrate with a short suprastapedial 
process. 
 Tylosaurus Marsh 
Cenomanian of New Zealand (Liodon Haamuriensis Hector). 
Upper Turonian of Kansas and New Mexico (Niobrara). 
? Senonian of New Jersey (Greensand). 
Hainsosaurus Dollo 
Upper Senonian of Belgium (Brown Phosphatic Chalk of 
Cipley). 
*Mem. Soc. Belg. Geol., iv. 168. 
tUeber the Pythonomorphen der Kansas Kreide, Paleontographica, xli, 36. 
