0. C. Marsh—New Characters of Mosasauroid Reptiles. 87 
separate the latter from the slender, distinct vomers. In the 
genus Tylosaurus, the posterior ends of the pterygoids form a 
distinct head. In Lestosaurus and Holosaurus, this extremity is 
broad and thin. In none of these genera were the pterygoids 
united by suture on the median line, but were more or less 
widely separated. 
The new characters above presented are all Lacertilian, rather 
than Ophidian. The important characters of the Mosasauroids 
now known indicate that they form a suborder of the Lacertilia, 
which should be called Mosasauria. 
Holosaurus abruptus, gen. et sp. nov. 
The type specimen on which the present genus is based is 
one of the most complete skeletons of the Mosasauroid reptiles 
yet discovered. This genus is most nearly related to Leséo- 
saurus, and agrees with it in the form and general characters of 
the skull. It may be readily distinguished by the coracoid, 
which is entirely without emarginations, as well as by other 
points of difference. From Tylosaurus it is separated widely 
by the premaxillaries, mandibles, and the palatines. 
_ The present species was one of the shortest in proportion to 
its bulk hitherto described, the skull and tail being both 
abruptly terminated. The entire length was about twenty 
feet. There are 98 vertebre preserved between the skull and 
a point in the tail where the caudals have a diameter of one 
inch. Many of these vertebre are in position. The caudals 
preserved all had articulated chevrons. 
me of the dimensions of the present specimen are as 
follows : 
Length of entire lower jaw (two feet) .....-..-.-- 610°™™ 
Length of dentary bone, on lower border..-...--- 342° 
Length of twelfth vertebin 2. ea 
Transverse diameter of ball......--..--.-------- 50° 
Length of twentieth vertebra ..........-.------- 85° 
Beboth Of humwiene 2200000 a oe 
ay Mie OC Gintal oh. ooo ae 
MeO Of fadtud. oo Oe 
sadn Of WA. a 88° 
Length of femu Slugs ee uo ae 
Width of distal end.2.0.00 2 oe 
mebigth of Gbule: eos ee ede: 117° 
Width of distal end... 0 See eeclaaes 100° 
Length OF UD a, ee 
Wrath of diatal and: soc. 2. ee 76° 
This specimen was found in the yellow Cretaceous chalk of 
Kansas, y Mr. S. W. Williston, of the Yale Museum. 
Yale College, New Haven, Dec. 20th, 1879. 
