R. S. Lull — Armor of Stegosaurus. 205 



or carina of the latter. This expanse is practically alike on 

 both sides, with blood-vessel impressions and no indication that 

 either one side or the other was in contact with the creature's 



Fig. 6. 



Fig. 6. Dermal plate of Ankylosaurus. Figured by Marsh as that of 

 Triceratops and showing the median carina, 1/8 natural size. 



flesh. On the other hand, the base, the morphological equiva- 

 lent of the body of the scute in crocodile or Ankylosaur, is 

 always somewhat asymmetrical even when divided into two 

 portions by the longitudinal cleft of those of the cervical 

 region. This base in the great dorsal plates particularly is 

 extremely rugous, implying either a heavy pad of cartilage or a 

 very thick connective tissue between the plate and its under- 

 lying skeletal support. There is in no instance any indication 

 of a true articulation with the subjacent bones. 



IV. Position of the akmoe. 



The position of the armor plates has given rise to an animated 

 discussion as to whether they were in one row or two, opposite 

 or alternating, erect or procumbent. The evidence seems to 

 point to a double row of paired, erect plates, though toward the 

 end of the tail the aggressive series evidently stood out at 

 a decided angle from the perpendicular. It is quite possible 

 that they were provided with an erectile musculature to give 

 them greater rigidity especially in time of use, as is the case 

 with the nasal horn of the rhinoceros. This seems to have been 

 particularly true of the tail. 



Professor Marsh (this Journal, xxxiv, 1887, p. 415), who first 

 described and figured the dermal armor of Stegosaurus, says : 

 "The upper portion of the neck, back of the skull, was protected 

 by plates arranged in pairs [italics mine] on either side. 

 These plates increased in size farther back and thus the trunk 

 was shielded from injury. From the pelvic region backward, 

 a series of huge plates stood upright along the median line, 

 gradually diminishing in size to about the middle of the tail." 



In his restoration of Stegosaurus (fig. 1), first published in 

 1891, however, Marsh places the entire series of plates in a 

 single row along the mid-line of neck, back, and tail, although 

 the caudal spines are represented as paired. 



