204 



i?. S. Lull — Armor of Stegosaurus. 



Stegosaurus ungulatus as represented by the specimen (Cat. 

 No. 1853) now being mounted at Yale was apparently the best 

 endowed with offensive weapons of any of its relatives, for there 

 are associated with the one skeleton no fewer than four pairs 

 of spines and three odd, sharp-edged, spine-like plates, one of 

 which is so much larger than the other two that it seems to 

 imply that at least one intervening size is missing. 



The spine-like plates are characterized by a very oblique, flat 

 base, by sharp edges fore and aft and, like the others, by the 

 impression of blood-vessels over the side expanse (fig. 4). In 



Fig. 4. 



Fig. 5. 



Fig. 4. Caudal spine-plate of Stegosaurus ungulatus. After Marsh. 

 1/12 natural size, a, side view; b, posterior view; c, section; d, inferior 

 view of base. 



Fig. 5. Caudal spine of Stegosaurus ungulatus. After Marsh. 1/12 

 natural size, a, side view; b, dorsal view; c, section; d, inferior view of base. 



common with the dorsal plates they give evidence of having 

 been deeply imbedded in the integument and underlying con- 

 nective tissue, but, unlike the latter, they show a better surface 

 for the attachment of muscles to give rigidity to their position. 

 Of the caudal spines (fig. 5) the anterior ones are the larger 

 and more deeply embedded, being lodged in a thicker portion 

 of the tail, and in common with all of the plates give evidence 

 of having been ensheathed with a close-fitting integument, 

 probably of a horny character as in the modern horned toads 

 (Phrynosoma) and in Moloch horridits. 



III. Morphology of the plates. 



Upon comparing a given plate with a scute of a crocodile, or 

 that of such a dinosaur as Anhylosaurus or Stegopelta, it at 

 once becomes apparent that the great expanse of the first rep- 

 resents merely an enormous hypertrophy of the median ridge 



