OSTEOLOGY OF THE AEMOBED DINOSAUBIA. 109 



Marsh says of these specimens: "Aside from the form of the skull [meaning 

 maxillae] these specimens have in the fore foot the intermediun 'and ulnar bones 

 separate, while in Stegosaurus these carpals are firmly coossified." As shown by 

 specimens in the National Musevun (fig. 36), all small individuals have the inter- 

 mediimi, ulnare, and pisiform separate, while in large individuals these are com- 

 pletely fused. Another character assigned to Diracodon is the freedom of the astrag- 

 alus and calcaneiun from tibia and fibula. This is also an age characteristic, as 

 abundantly shown by National Museum specimens. The caudal vertebrae and spines 

 ascribed to D. laticeps by Marsh (pi. 15) agree in shape and size with those belonging 

 to Stegosaurus, and are here referred to S. stenops (compare pis. 15 and 16). From 

 this brief review it will be seen that this genus and species rests entirely upon the 

 characters displayed by the teeth and maxillary bones, and these, accordmg to the 

 description by Marsh, agree in nearly all respects with those of Stegosaurus. In 

 1902 Zittel's Text-book of Paleontology (vol. 2, p. 242) says: "Is probably founded 

 on the young of this species," referring to S. ungulatus. It appears that at the 

 time Diracodon laticeps was founded the homologous parts of Stegosaurus were 

 unknown, which would accoimt for Marsh's statement that the genus is most 

 nearly related to Laosaurus, and also for its reference to the Family Camptosau- 

 ridse (Camptonotidse) , an assignment corrected later. 



Although I have not had an opportunity of examining the type-specimen, it 

 would appear that the genus, and probably also the species, are invaUd and should 

 be abandoned. 



STEGOSAURUS SUtCATUS Marsh. 



Plates 18; 20, figs. 3 and 4; 21, fig. 2; 23, fig. 1; 25, fig. 3. 



Stegosaurus sulcatus Marsh, Amer. Jouru. Sci., vol. 34, 1887, p. 415, pi. 8, figs. 4-6; Geol. Mag., 

 ser. 3, vol. 5, 1888, pi. 2, figs. 4-6; Sixteenth Ann. Rept. U. vS. Geol. Survey, pt. 1, 1896, pi. 

 50, figs. 4-6.— NopcsA, Foldtani Kozlony, Budapest, vol. 31, 1901, p. 215.— Hay, Bull. 179, 

 U.' S. Geol. Survey, 1901, p. 496.— Lull, Amer. Journ. Sci., vol. 29, 1910, pp. 209, 210, fig. 11. 



Type-specimen.— Cat. No. 4937, U.S.N.M. Consists of 4 dermal spines, 2 

 dermal plates (one pertaining to the neck, the other to the mid-dorsal region), 

 right humerus, right ulna, two radii, both fore feet, portions of both scapulae, 

 parts of femora, fibula, ischium, and caudal vertebrae. Collected by Mr. J. L. 

 Kenney in 1883. 



Type-locality.— QiiurT J 13 near Como, vUbany County, Wyoming. 



Horizon. — Morrison, Upper Jurassic. 



Description. — This species has never been adequately defined, and it is only 

 recently that the type-specimen was assembled and prepared for study. Marsh 

 confined his first observations to a study of one of the dermal spines of the ante- 

 rior pair. Two grooves or sulci (pi. 18, fig. 2) on the inner face suggested the 

 specific name, but, as will be shown later, these grooves are not present on the 

 opposite spine, and this character, therefore, does not serve to distinguish the species. 



The original description is as follows : 

 In one large species, which maybe called Stegosaurus sulcatus, there is at present evidence of only 

 one pair of spines. These are the most massive of any yet found, and have two grooves on the inner 

 face, which distinguish them at once from all others known. 



