Apr. 1903. North American Plesiosaurs — WiLLlSTON. 51 



by the aid of a nearly complete paddle of another species, described 

 further on. This paddle was less compressed and distorted, and I 

 have therefore reserved it for a more full description of the parts and 

 discussion of the functions. 



The humerus of Dolichorhynchops has the head only moderately 

 convex, with its margins rather sharply limited, its greater convexity, 

 as usual, on the radial side; its general surface looks mesad and 

 ventrad at an angle of about forty-five degrees. Its cartilaginous 

 surface is continuous with that of the tuberosity, which has a large, 

 flat surface, directed dorsad and mesad at an angle of about forty-five 

 degrees. The grooves separating the surface from the head are 

 broad and shallow, that of the ulnar side the broader. The anterior 

 border of the bone is concave on the proximal part, gently convex at 

 the middle and shallowly concave on the distal part. The posterior 

 border is nearly straight on the shaft, deeply concave distally. The 

 distal anterior angle is rounded in both specimens. On the distal 

 border two facets are apparent, for the radius and ulna; the rest of 

 this border presents no clear indications of articulations. The 

 pectoral rugosity is strongly roughened, and produced into a broad, 

 low tubercle; the roughening, moreover, is continued obliquely nearly 

 to the other rugosities on the sides. It is situated nearer the head 

 than in Polycotylus. The ulnar rugosity forms a deep pit above the 

 middle of tlie bone, while the radial rugosity is opposite it and much 

 nearer the head of the bone than in Polycotylus. 



Three bones were certainly located in the fore-arm, and a fourth 

 one seems to be represented by a pair of small nodules. The free, 

 emarginate border between the radius and ulna is less apparent than 

 it is in Polycotylus. The relations of all the smaller bones seem to 

 be quite as they are in Polvcotvlus. and the reader is referred to the 

 figures of the two paddles for comparison, in connection with the 

 description of that of Polycotylus. » 



Hind Limbs. — The femur shows the usual plesiosaurian differences 

 from the humerus, in its greater slenderness, slightly greater length, 

 tnore slender shaft and less dilated distal extremity. The anterior 

 border, as seen in the figure, is nearly uniformly concave, terminating 

 in a more pronounced angle than in the humerus. The posterior 

 border is, also, concave throughout to the greatest expansion, which 

 occurs more proximally than in the humerus, and in a rather better 

 marked angle. The rugosities of the under side and margins art as 

 in the humerus, though scarcely as well marked. Whether the bones 

 of the leg and ankle have been correctly located, rather than in the 



