158 University of Kansas Geological Survey. 



ately constricted, and the proximal extremity is but little more 

 expanded than the distal, and both but slightly convex. The 

 fifth is a broader and shorter bone than the others, divaricate, 

 as in the other genera, but with the broader extremity proxi- 

 mally. Its proximal articular border is oblique, and the inner 

 border is shorter and more deeply concave than the outer. 



Phalanges. 



Clidastes. The phalanges of Clidastes offer distinctive char- 

 acters from those of the other genera, which will usually per- 

 mit them to be referred to this genus without trouble. They are 

 smoother and more sharply truncate at the extremities, the ends 

 being flat or even concave. In the first finger there are four, 

 more flattened and expanded than in the next three fingers. 

 The first is broadly expanded proximally to correspond with the 

 distal extremity of the metacarpal. The remaining three of the 

 first may be distinguished from those of the next three fingers 

 by the outer distal angle being thinned and rounded. In the 

 fifth finger there are three ; the first is flattened and much ex- 

 panded proximally, but is shorter than the corresponding bone 

 of the first finger. The second is not three times the length of 

 its proximal extremity, and all, like those of the first finger, 

 have a distal angle rounded. In the second, third and fourth 

 fingers there are four or five phalanges, all of which are rather 

 slender, markedly constricted, and with their extremities nearly 

 symmetrical. 



Platecarpus. In Platecarpus the phalanges resemble those of 

 Clidastes more closely than those of Tylosaurus, and seem to be 

 the same in number or but one or two more in the middle fin- 

 gers. The bones of the first and fifth fingers are more flattened 

 and unsymmetrical than in the other fingers, but less so than 

 in Clidastes. In plate xliv is shown a paddle of P. ictericus drawn 

 by myself many years ago, as the bones lay in position. 



Tylosaurus. In Tylosaurus the phalanges are more slender 

 than in either of the other genera, and much more numerous. 

 A specimen in the museum of T. proriger, from which the char- 

 acters of the paddles have chiefly been derived, has the front 



