416 0. 0. Marsh — Characters of the order Hallopoda. 



In size, the animal was about as large as a rabbit, but the 

 fore limbs were proportionately much smaller. As the present 

 specimen is the only one known, it is important to place on 

 record its distinctive characters. 



The scapula is of moderate length, and its upper portion 

 broad and thin. The humerus is slender, with a strong radial 

 crest. The shaft is very hollow, with thin walls, and the cavity 

 extends almost to the distal end. The latter is but little ex- 

 panded transversely. The radius and ulna are short, and were 

 closely applied to each other. There were but four digits in 

 the manus, the first being short and stout, and the others 

 slender. 



All three pelvic bones aided in forming the acetabulum, as 

 in typical Dinosaurs. The ilia are of the carnivorous type, 

 and resemble in form those of Megalosaurus. The pubes are 

 rod-like, and projected downward and forward. The distal 

 ends are closely applied to each other, but not materially 

 expanded, and in the present specimen are not coossified 

 with each other. The ischia projected downward and back- 

 ward, and their distal extremities are expanded, somewhat as 

 in the Crocodilia. 



The femur is comparatively short, with the shaft curved and 

 very hollow. The tibia is nearly straight, much longer than 

 the femur, and its shaft equally hollow. The fibula was 

 slender and complete, but tapered much from above downward. 

 Its position was not in front of the tibia below, as in all known 

 Dinosaurs, but its lower extremity was outside, and apparently 

 somewhat behind, the tibia. 



The astragalus is large, and covered the entire end of the 

 tibia, but was not coossified with it. The calcaneum is com- 

 pressed transversely, and much produced backward. It was 

 closely applied to the outside of the astragalus, and although 

 agreeing in general form with that of a crocodile, strongly 

 resembles the corresponding bone in some mammals. The 

 tarsal joint was below the astragalus and calcaneum. There 

 appears to be but a single bone in the second tarsal row, 

 although this may be composed of two or more elements. 



There were but three functional digits in the hind foot, and' 

 their metatarsals are greatly elongated. The first digit was 

 entirely wanting, and the fifth is represented only by a remnant 

 of the metatarsal. The posterior limbs, as a whole, were 

 especially adapted for leaping, and are more slender than in 

 almost any other known reptile. 



