AND AVES OF NORTH AMERICA. 91 



number of the metatarsals. Thus so far as known, according to Owen, Hylaeosaurus 

 Mant. had three closely approximate metatarsals. In Hadrosaurus they are elongate, but 

 their number is unknown. In Iguanodon, Owen represents a fourth, but nidi mental 

 metatarsal, the hind foot being still three-toed, while in the more ancient genus Scelido- 

 saurus, the same authority gives four shortened metatarsals, of which the smallest supports 

 a digit ; and a fifth rudimental metatarsus, which supports no digit. In Stenopelix there 

 appear to be five digit bearing metatarsals according to Von Meyer. 

 This order is then probably divisible into the following families : 



I. Teeth in several rows forming a vertical pavement ; metatarsals "? three. 



HADROSAURIDAE. 



Embracing the genus Hadrosaurus, Leidy. 



II. Teeth in a single row, cutting ; three digit bearing metatarsals. 



IGUANODONTIDAE. 



Genera Iguanodon Buckl. Hylaeosaurus Mant. 1 Palaeoscincus, Leidy. 



III. Teeth in a single row, cutting ; four digit bearing metatarsals. 



SCELIDOSAURIDAE. 



Genera Scelidosaurus, Owen. Stenopelix Myr. (Heeth). The last named genus is 

 known from a single skeleton, in which according to Von Meyer, the sacral vertebras are 

 aU distinct. It is perhaps an immature individual. 



HADROSAURUS, Leidy. 



Proc. Ac. Nat. Sci. Phila., 1858, 218. Cretaceous Reptiles N. Am., 7G. Trachodon, Leidy, L. C. 1S56. ? Thes- 

 pesius, Leidy 1. c. 



This genus embraces at least two species which are among the most gigantic terrestrial 

 animals of which we have any knowledge. They represent the Iguanodon of the old 

 continent, whose species is similar in bulk. The two genera, however, differ in many 

 details. The teeth, as above noted, are different. The spines of the dorsal vertebrae, 

 instead of being flat anteriorly, are smaller and slender subcylindric. 



Most of the characters of this genus have been given by Leidy in his description of 

 H. foidkii. I add a more complete examination into the characters of the scapular and 

 pelvic arches, which are but lightly treated of in the " Cretaceous Reptiles of N. America." 



Scapula. — Here may be introduced a description of certain massive bones of two indi- 

 viduals of a species of Dinosaur. I had formerly admitted the possibdity of their 

 pertinence to the pelvis of Hadrosaurus, but the discovery of that element in the H. 

 foulkei, indicates that another place must be sought for them. 



