72 BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



Measurements of calcaneum of Antrodemus valens Leidy. No. 4734, U.S.N. M. 



mm. 



Greatest length (antero-posterior) 65 



Greatest height 53 



Greatest breadth 4 



Astragalus (As.).— Id. specimen No. 4734, U.S.N.M., the left astragalus is 

 firmly conjoined, if not actually coossified, with the tibia. A detached left astrag- 

 alus, No. 7336, U.S.N.M., from "Quarry No. 1," Canon City, Colorado, which 

 clearly shows all of the principal features of this element, is the basis for the de- 

 tailed description given below. 



Viewed from the front, the astragalus consists of a heavy rectangular lower 

 portion from which rises 



on its outer half a wide, j 



thin ascending process. /^M)k 



At the base it is slightly /fWfc- 



more than half as wide / |jf ffl 



as the lower portion ^V' ' ,l >%^_ 

 from which it springs. / * lllllt~ 

 In outline this process is V^i 

 angular, narrowing ^^^ 

 rapidly toward the top. 



The anterior face is set £ x-K-^a /$[ 



back from the heavier /mnTw 1 ^ /fl<h. 



articular portion below mmlnwAi^ W-l 



and is further defined by /jjd |ft if ® 



pods, where it reaches ^^va 



its maximum develop- fig. SO.— Left astragalus of Antrodemus valens Leidy. No. 7336, TJ.S.N.M. } nat. 

 ment and the Triassic SIZE ' A ' ANTERI0E view; B, dorsal view; C, external view. Ca, articular 

 ' . surface for calcaneum. 



theropods, where it is 



entirely absent, shows a progressive development of this process during successive 



geological periods. 



The main lower portion of the astragalus at about its center on the anterior 

 face is traversed by a shaUow transverse groove, which deepens toward the inner 

 margin, and which turns downward slightly toward the external border when it ends 

 at the base of a deep notch. 



Viewed from above the surface on which the tibia rests is broadly concave 

 antero-posteriorly on the inner half, but on the outer half rapidly narrows becoming 

 V-shaped. At the base of the ascending process on the posterior side is a large 

 circular depression in the bone that at first glance gives the impression of being a 

 foramen. The inner end is heavy and obliquely truncated to the longer transverse 



