640 



SCIENCE PROGRESS 



both from the Upper Cretaceous beds of Edmonton, Alberta, 

 Canada. The type skeleton of the first of these, which measures 

 about 32 ft. in length, or nearly the same as that of the con- 

 temporaneous Trackodon mirabilis, has been mounted on a 

 slab for exhibition in the American Museum. This genus, it 

 appears, is much more numerously represented in the Edmonton 

 beds than is its cousin Trackodon. The skeleton of the second 



Fig. 2. — Lateral (A) and posterior (B) 

 aspects of dorsal vertebrae of 

 Hypacrosaurus alttspinis. 



(From Bull. Amer. Mus. Nat. Hist.) 



Fig. 3. — Skeleton of the left hind 

 limbs of Trackodon (A) and 

 Hypacrosaurus (B). 



(From Bull. Amer. Mus. Nat. Hist.) 



genus, Hypacrosaurus, is characterised by the great height of 

 the spines of the dorsal vertebrae (fig. 2), coupled with the 

 presence of nine vertebras in the sacrum, against eight in the 

 allied genus. In all the members of the family the hind limbs 

 were tridactylate ; the distinctive features of those of Trackodon 

 and Hypacrosaurus being shown in fig. 3. 



The skeleton of the fore-limb of a species of Trackodon from 



