NO. 2120. THE FORE LIMB OF ALLOSAURUS FRAGILIS—GILMORE. 511 



pointed claws, the first being especially robust, the third much 

 reduced in size. The proximal phalanx of digit one is the longest of 

 the series. The proximal articular surface is concave supero- 

 inferiorly, with a strongly developed vertical keel which articulates 

 with the deep groove on the distal end of mtc. I. This keel as 

 shown in figure 7c, divides this articular end into two unequal 

 concave surfaces, the larger one being toward the outer side of the 

 foot. [It is incHned to the vertical axis of the bone and when 

 articulated rotates the distal end so that the ungual phalanx is 

 turned inward from the vertical as shown in figure 2. The articular 

 surface for the claw is broadly grooved, and this surface extends well 

 backward on the under side, thus throwing the articulated imgual 

 downward at nearly a right angle to the longer axis of the first 

 phalanx. The lateral pits are comparatively shallow, the one on the 

 external side being the better defined. Viewed from above the shaft 

 is quite evenly rounded transversely, while the ventral surface pre- 

 sents a flattened aspect. The ungual of digit one is especially 

 robust, with a regularly curved and sharply pointed extremity. 

 Well-defined lateral grooves run back from the tip on both sides, 

 but as they approach the proximal end curve downward, passing 

 into a broad smooth surface on the posterior ventral surface. The 

 proximal articular surface is keeled as shown in figure 7&. 



The proximal phalanx of digit two is shorter than the second of that 

 toe. The proximal end of the former is expanded especially in the 

 vertical direction. The proximal end as compared with the same pha- 

 lanx of digit one is only shghtly concave supero-inf eriorly with a com- 

 paratively low obtuse keel, placed more toward the inside of this end. 

 Like the keel on the proximal phalanx of digit one it is placed at an 

 angle to the vertical axis of the bone. The concave lateral depres- 

 sions on either side near the distal extremity are so shallow and iUy 

 defined they could hardly be designated as pits. The second pha- 

 lanx of this digit is slightly longer than the first, with a sharply 

 keeled proximal end and broadly grooved distal articulating surface. 

 The lateral pits are small but well defined. The ungual phalanx is 

 intermediate in size between those of the first and third toes. 



The proximal phalanx of digit three can be distinguished from all 

 others in the foot by the keelless, but cupped articular surface of the 

 proximal end (fig. 7a). It is relatively short, as is the second, the 

 third being more elongate. The proximal ends of the other phalanges 

 of this toe are keeled, and the distal ends are grooved. The ungual 

 except for its small size is very similar to the ungual of digit two. 

 These two unguals are distinguishable from the ungual of digit one, 

 not only by difference in size but also by the change in direction of 

 the heavy portion below the articulating surface. In the two former 

 in the articulated foot it looks almost directly backward, whereas in 



