maksh.1 CCELURUS. 155 



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 calcaueum. 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 seems to be 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. 



The main characters of the posterior limb are shown in fig. 3, on the 

 opposite page, which represents the bones of the left leg and foot, nat- 

 ural size, in the position in which they lay when uncovered. All the 

 bones figured are still firmly embedded in the matrix. 



There are but two vertebra? in the sacrum. The other vertebras pre- 

 served have their articular faces biconcave. The chevrons are slender 

 and very elongate. 



Taken together, the known characters of Hallopus clearly indicate 

 dinosauriau affinities rather than those of any other group of reptiles, 

 aud if the Dinosauria are considered a subclass the Hallopoda at pres- 

 ent may be regarded as a group of dinosaurs standing further apart 

 from typical forms than any other. 



CCELURUS. 



In the horizon above, the Atlantosaurus beds of the upper Jurassic, 

 the carnivorous dinosaurs are of larger size, aud some of them were 

 among the most powerful and ferocious reptiles known. The one 

 nearest Hallopus in size and general characteristics is Ccelurus, 

 described by the writer in 1879 and now known from several skeletons, 

 although no good skull has yet been discovered. 



The skull of Coelurus is known only from fragments. The teeth are 

 typical of the order Theropoda. One is shown on PI. VII, fig. 1. The 

 most marked feature in all the known remains of Ccelurus is the 

 extreme lightness of the bones, the excavations in them being more 

 extensive than in the skeleton of any other known vertebrate. In the 

 vertebra?, for example, the cavities are proportionately larger than in 

 either pterodactyls or birds, the amount of osseous tissue retained being 

 mainly confined to their exterior walls. In PI. VII cervical, dorsal, 

 and caudal vertebra? are figured, with transverse sections of each to 

 illustrate this point. Even the ribs of Ccelurus are hollow, with well- 

 defined walls to their large cavities. 



THE VERTEBR/E. 



The vertebra? of Ccelurus now known are from various parts of the 

 column, and most of them are in good condition. Three of these are 

 represented, natural size, in PI. VII. The cervicals are large and elon- 



