110 



BULLETIN 89, UNITED STATES NATIONAL MUSEUM. 



In some trays of unprepared material in the United States National Museum 

 there was found, together with other parts of the skeleton, three dermal tail spines, 

 one of which (6, fig. 65) bore a striking resemblance to the spine figured and described 

 by Marsh as the type of S. sulcatus, its chief difference from the type being the 

 absence of the "two grooves on the inner face." In the same tray was a box 

 label, on which was written, with other information, evidently by the collector, 

 "four spines in this box." Since only three were found, it occurred to me that 

 perhaps the fourth might be the one described by Professor Marsh, and upon com- 

 paring the original labels found with each the above conclusion was verified. Both 

 labels had the accession number |1650| , and they also showed that all four of the 

 spines had been packed in " box 8 " when shipped from the field. This information, 

 together with the fact that of the 30 dermal spines now before me, there is only 

 one (this in the "box 8" lot) showing a resemblance to the type spine of S. sulcatus 

 through the great development of the basal end. There was also the additional 



Fig. 65.— Anterior pair op dermal tail spines of Stegosaurus sulcatus Marsh. Type. Cat. no. 4937 U.S.N.M. 

 About t v nat. size. Viewed prom the front, a, Type spine; 6, spine recently found; c, rugose surface for 

 cartilagious union of the two spines above the caudals; /, foramen passing into interior of spine; s, sulci, 

 present only on right-hand spine. 



evidence of this being the proper association of these bones from the fact that 

 these two spines are opposites, as shown in figure 65. The posterior dermal spines 

 lack the greatly enlarged bases of the anterior pair, are without sulci (pi. 25, 

 fig. 3), and indistinguishable from those of an adult specimen of S. ungulatus. 



The type of S. sulcatus is a large and evidently a very old individual. The 

 few bones of this specimen sufficiently complete to be compared with those of 

 other species show no good distinguishing characters except for their very large size, 

 so that for the present this species must rest upon the greatly expanded bases of the 

 anterior pair of spines, and this feature may be found to be an age characteristic. 

 In that event this species would represent a very large and old individual of S. ungu- 

 latus. The sulci mentioned by Marsh and so plainly shown in plate 18, figures 

 2 and 3, are not present on the opposite spine, and in the Stegosauria this feature 

 is probably as inconstant as it has been found to be in the Ceratopsia, where sulci 

 are present on one supraorbital horn-core but absent on the other. These spines 

 are fully iUustrated in plate and text and further description appears unnecessary. 

 The radius, foot, and ulna are shown in plate 20, figures 3A, 4A, plate 21, figure 2, 

 and nuchal plate in plate 23, figure 1, also in text figure 57. 



