416 0. C. Harsh — Skull and Armor of Stegosaurus. 



The American genera of the Stegosauria are Stegosaurus 

 and Diracodon. Of the former, there are several well-marked 

 species besides S . armatus, the type. Of the latter genus, 

 but one is known at present, Diracodon laticeps, the remains 

 of which have hitherto been found at a single locality only, 

 where several individuals referred to this species have been dis- 

 covered. Aside from the form of the skull, these specimens 

 have in the fore foot the intermedian and ulnar bones separate, 

 while in Stegosaurus, these carpals are firmly coossified. 



All the known American forms appear to have the second 

 row of carpals unossified, and five digits in the manus. In the 

 hind foot, the astragalus is always coossified with the 'tibia, 

 even in very young specimens, while the calcaneum is some- 

 times free. The second row of tarsals is not ossified in any of 

 the known specimens. Only four digits in the hind foot are 

 known with certainty, and one of these is quite small. All 

 forms have at least three well- developed metatarsals, which 

 are short and massive, but longer and much larger than the 

 metacarpals. Most of the bones originally referred to the 

 hind foot of Stegosaurus ungidatus, and figured as such 

 (this Journal, vol. xxi, Plate VIII), although found with the 

 posterior extremities, subsequently proved to belong to the fore 

 foot of another larger species. 



In one large specimen, of which the posterior half of the 

 skeleton was secured, no trace of dermal armor of any kind 

 was found. If present during life, as indicated by the massive 

 spines of the vertebrae, it is difficult to account for its absence 

 when the remains were found, unless, indeed, the dermal cover- 

 ing had been removed after the death of the animal, and 

 previous to the entombment of the skeleton where found. In 

 this animal, the ilia were firmly coossified with the sacrum, 

 thus forming a strong bony roof over the pelvic region, as in 

 birds. 



This specimen represents a distinct species, which may be 

 called Stegosaurus duplex. It was originally referred by the 

 writer to S. ungxdatus, and the pelvic arch figured under that 

 name.* In the sacrum of this species, each vertebra supports 

 its own transverse process, or rib, as in the Sauropoda, while 

 in S. ungulatus, the sacral ribs have shifted somewhat forward, 

 so that they touch, also, the vertebra in front, thus showing an 

 approach to some of the Ornithopoda. 



*This Journal, vol. xxi, Plate VII, Feb., 1881. 



