no 



A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA 



Dtadectidte. The condyles are not well developed; the articular face on the proxi- 

 mal end is not distinct. 



The shaft is slender and has a triangular section. There is a distinct entepi- 

 condylar process, an entepicondylar foramen, and a well-marked hemispherical 

 articular process for the head of the radius, almost entirely on the anterior surface 

 of the bone. In the descriptions o( Labidosaurus by Case and Williston the humerus 

 was described as not having an entepicondylar foramen, but this was an error due 

 to the condition of the specimen. 



Only the proximal ends of the ulna and radius are known. The first shows a 

 definite, but not well-developed olecranon process. "The front foot (fig. 48, J) of 

 the left side has been preserved; the distal ends of the radius and ulna are nearly in 

 their normal positions; the bones of the carpus are all present, with the possible 

 exception of the first carpal of the distal row. There are well-formed scaphoid and 

 cuneiform bones, and between these an elongate element that was at first regarded as 

 the missing metacarpal I, but it seems more probable that it is the lunare (inter- 

 medium); the upper end is incomplete, and the lower is much the same in appearance 

 as the end of the metacarpals; on the other hand, it occupies just the position of the 



Fig. 49. — Labidosaurui. No. 4883 Am. Mus. X J. 



A. Distal portion of the tarsus. Dorsal surface. 



B. Ventral surface of same. 



C. Restoration of tarsus. After Williston. 



intermedium, in a carpus that has been preserved in a very perfect manner, and it 

 fits the position it occupies very accurately. According to this interpretation there 

 are two centrale. There are four bones in the distal row of the carpus; the first 

 is very much larger than the others, and appears to represent the first and second 

 combined; the outer edge is a rounded process, with no face for articulation with 

 another carpal. It is possible that the first metacarpal was attached to this bone 

 with the second, but no traces of such a metacarpal remain. The metacarpals are 

 short and stout, with well-developed articular condyles. The phalanges are not 

 in contact with metacarpals, but a series which corresponds very closely to the 

 fourth in size shows that they were also very short and strong. It is impossible to 

 say whether there were more than three phalanges or not. Fig. 48J (of this paper) 

 shows the arrangement of the bones very little altered from their position in the 

 matrix." (Case, II.) 



The posterior limb and foot (plate 8, figs. 7, 8a, 8^, and fig. 48): The femur is 

 short, but well formed. There is a deep concavity on the posterior surface and 

 a prominent trochanter with a short rugose ridge at its lower end. The distal 

 articular surface is not divided by a median groove, as in the Pelycosauria, but 

 presents distinct faces for the tibia and fibula. The tibia is short, with proximal and 

 distal ends equally expanded. There is the usual deep groove on the anterior 



