Williston.] Mosasaurs. 193 



I give the original description, as follows : 



Holosaurus abruptus Marsh, I.e. "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 Lestosaurus [Platecarpus] , and 

 agrees with it in the form and general characters of the skull. 

 It may be readily distinguished by the coracoid, which is en- 

 tirely 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 the bulk hitherto described, the skull and tail being both 

 abruptly terminated. The entire length was about twenty 

 feet. There are ninety-eight vertebras preserved between the 

 skull and a point in the tail where the caudals have a diameter 

 of one inch. Many of these vertebras are in position. The 

 caudals preserved all have articulated chevrons. 



"Some of the dimensions of the present specimen are as 

 follows : 



' ' Length of entire lower jaw ( two feet ) . . 610 mm. 



Length of dentary bone on lower border 342 



Length of twelfth vertebra 71 



Transverse diameter of ball 50 



Length of twentieth vertebra 85 



Length of humerus 146 



-Width of distal end 136 



Length of radius 102 



Length of ulna 88 



Length of femur 141 



Width of distal end 85 



Length of fibula 117 



Width of distal end 100 



Length of tibia 99 



Width of distal end 76 



This specimen was found by myself in the yellow chalk of 

 Butte creek, Kansas, iu the summer of 1877. 



The estimate of the length is clearly too great. If the pro- 

 portions are as in the species of Platecarpus it would not be over 

 sixteen feet in length. The vertebras do not vary a great deal 

 in length to the base of the tail, or about the thirtieth vertebra. 



