JR. S. Lull — Armor of Stegosaurus. 



203 



ward from the apex of the jaw, the largest of them being not 

 less than 25 mra in diameter. 



. The dorsal armor consists in turn of four distinct shapes, two 

 apparently defensive and two offensive, with a marked differ- 

 entiation in form as well as in function. Of these the first 

 (fig. 2) are more or less oval, with a base divided longitudinally 



Fig. 2. 



Fig. 2. Cervical plate of Stegosaurus ungulatus. After Marsh. 1/12 

 natural size, a, side view; b, inferior view of base ; c, opposite side; d, thin 

 margin; e, rugous bases; /and/ 1 , surface marked by vascular grooves. 



by a deep cleft so as to be distinctly bifid and of very short fore 

 and aft extent compared with the expanse of the plate. These 

 plates show a very rapid increase in size, though the largest of 

 them in Stegosaurus ungulatus is only about half the height 

 and one-third the antero-posterior diameter of the largest of the 

 next type. These bifid based plates seem to have been borne 

 on the neck, the largest oval one here figured (fig. 2) being 

 near the point of junction between the neck and the trunk. 



The second type are the large, thin, rectangular or somewhat 

 triangular plates with a thick base but without the median 

 longitudinal cleft. They doubtless stood in pairs along the 

 trunk region and upon the proximal portion of the tail (fig. 3). 



Fig. 3. 



Fig. 3. Dorsal plate of Stegosaurus ungulatus. After Marsh. 1/12 

 natural size, a, right side ; b, thick basal margin ; c, leftside; other letters 

 as in fi». 2. 



