168 University of Kansas Geological Survey. 



Platecarpus. The metatarsals of Platecarpus are better known 

 than those of Clidastes. The first is the most expanded at the 

 base ; the second, third and fourth less so, resembling the pha- 

 langes. The fifth is most characteristic; it is thin and flat- 

 tened, with the proximal extremity much expanded, gently- 

 convex and a little oblique. The distal or outer border is more 

 thickened than the opposite, and is concave throughout. The 

 inner or proximal border is thin and slightly concave from the 

 prominent flattened rounded proximal angle. The distal ex- 

 tremity is less than half the width of the proximal, and is only 

 moderately thickened. It is slightly oblique to the long axis 

 of the bone. 



Tylosaurus proriger. In Tylosaurus the first and apparently 

 the fourth metatarsals are nearly symmetrical bones, with the 

 base broadly expanded and convex in outline. The fifth is 

 very much smaller — smaller relatively than in Platecarpus, 

 which it resembles. It is shorter than in that genus, the ex- 

 tremities more oblique. The proximal articular surface is 

 placed at an angle of about forty-five degrees with the long axis 

 of the bone. The outer border is short and deeply concave, and 

 thicker than the inner border. The latter is thin, short, and 

 shallowly concave between the broadly rounded angles. The 

 distal extremity is only a little narrower than the proximal ; it 

 is gently convex, and nearly transverse to the long axis of the 

 bone. The bone is not twice as long as wide. 



Phalanges. 



Clidastes. The phalanges in this genus are of the same gen- 

 eral character as those of the hand. Nothing is known of their 

 number and arrangement. In all probability the digits are of 

 a length similar to that in the hand. 



Platecarpus. The number of phalanges in the first and fifth 

 toes is probably four, and in the other toes five or six. In their 

 general character they resemble those of the front foot. 



Tylosaurus. The best information we have concerning the 

 hind paddle of this genus is the specimen of which a photo- 

 graphic illustration is given (plate l) . In all probability 



