408 G. R, Wieland — Archelon ischyros. 



of the proximal. The articular surfaces are in area and outline 

 nearly similar, except that owin^ to the concavity just men- 

 tioned the distal face is very slightly crescentic. In its gen- 

 eral aspect it is concave and divided by a saddle-shaped antero- 

 posterior ridge into two subequal areas, the exterior and 

 smaller being somewhat elliptical, the interior and larger 

 double concave in outline. 



The surface striations are not so distinct as those of the 

 humerus, tending to flatten and interlace. There is very slight 

 pitting and grooving with a tendency to fluting at the extremi- 

 ties, especially the distal. When closely examined witn a 

 reading glass the surface is found to be quite ornate. 



The ulna is a very compact bone of great strength and the 

 unequal size as compared with the humerus is apparent rather 

 than real. Taken as a homologous part of the huge forelimb 

 that formed the propeller of the largest known marine testu- 

 dinate, it was admirably adapted to its purpose. 



Radius. — The radius, like the ulna, is short and its pecu- 

 liar distal bow served to give width to the forearm without 

 reducing its strength. The outline of the distal articular sur- 

 face is that of an isosceles right triangle with the vertex 

 external. It is but slightly concave centrally. 



The surface is like that of the radius except along the 

 anterior edge, which is slightly rugose along its entire length. 



The set of the distal faces of the radius and ulna was slightly 

 toward each other and they formed a strong base for the mas- 

 sive carpals. Of these one is figured. The phalanges recovered 

 are not of unusual length. Several are ^gured. 



Measurements of the Ulna. 



Meters. 



Length .. -33 



Proximal diameters -088 and "138 



Least diameters of shaft _ _ '054 and '063 



Distal diameters '093 and '14 



Measurements of the Radius. 



Length (greatest) _ - '35 



Proximal diameters . . . i '049 and "088 . 



Distal diameters __ -082 and -114 



Least diameters of shaft "05 and '067 



Femur. — The femur is proportioned to the humerus as in 

 Thalassochelys earetta. The head stands out at a full right 

 angle on a heavy neck, high and prominent, the articular sur- 

 face being very convex ovally, the largest diameter bearing an 

 angle of about 45° to the main axis of the humerus. The 

 great trochanter rises well above the head as a somewhat semi- 



