366 R. S. Lull—Stegosani'UN uiu/nlatus Marsh. 



rib, as in the Saurojjoda, while in the S. ungxdatus tlic sacral 

 ribs have shifted somewhat forward, so that tliey touch, also, 

 the vertebi'a in front, thus showing an a]")proach to some of the 

 Ornithopoihi.'''' The specimen JSlo. 1853 contains uo sacral 

 parts e.\ce])t the ischia ; the above contrast being made, there- 

 fore, not with the other original type of *S'. nngulattis, but with 

 an entirely new sacrum of a much younger individual (No. 

 1857) arbitrarily referred to that species. In this specimen, 

 the sacral ribs are by no means as robust as in the older animal 

 representing the type of S. dxtplex, and even in the latter a 

 bearing of the rib against the preceding centrum may be 

 observed. In other words, the difference is merely one of 

 degree, which may readily be accounted for on the ground of 

 relative age. The distinction in the form of the ischiumi of 

 the type 1853 aud those of the specimen 1858, which Marsli 

 removed to 8. duplex, is slight, the difference being mainly in 

 a greater robustness especially in the distal end in the latter, 

 which may readily be an age, sexual or even an individual 

 variation. The two individuals embraced in the mount were 

 much alike, as far as one may judge, differing mainly in pro- 

 portions, No. 1853 being slightly longer and slenderer of limb. 

 The above evidence was submitted to Professors Osborn and 

 Willistou and to Messrs. F. A. Lucas and C. W. Gil more, the 

 question being as to the advisability of combining the speci- 

 mens iu a single mount. The unanimous conclusion was that 

 the validity of the species S. duplex was not proven, as the 

 specific characters mentioned could not be contrasted with 

 those of the remaining type of S. ungidatics, and that one was 

 abundantly justified in referring the so called type of xS'. duplex 

 back to its former status as a cotype of S. wngulatus, and, 

 further, in combining the two supplemental cotypes in a single 

 erection to represent the species and genus as originally 

 described. Thus the skeleton stands, a few missing bones 

 being modeled in plaster either from their fellows of the oppo- 

 site side or from another very complete though smaller speci- 

 men known in the museum as '■'■ Stegosaurus 1^," catalogue 

 number 1856. 



II. The Skeleton. 



Some of the most notable anatomical features are the remark- 

 able proportions of the animal with the sharply arched verte- 

 bral column, short neck, small head, lank, narrow body and 

 extremely long limbs. The tail, which did not droop abruptly 

 as represented in all previous restorations, was evidently held 

 high above the ground and gives evidence, especially in its 

 posterior half, of extreme sinuous flexibility, and, armed as it 

 was with sharp-edged plates and spines, was the principal 

 weapon of offense and defense against tiie sanguinary car- 

 nivores of that day. 



