THE SKELETON OF TRIMERORHACHIS 293 



mens is the presence of a thin bony skin or armor closely 

 sheathing the whole body, with the exception of the skull and 

 clavicular girdle. As the cadaver came to rest it was immersed 

 in the soft mud to near its middle. The skin lining the cavity thus 

 made retains its original position. On the decay of the body, the 

 bones fell to the lower part, closely covered everywhere by the skin 

 of the upper part of the body. On the right side the skin had 

 bulged outward near the middle. When first uncovered the bones 

 were concealed everywhere by the skin. It has been removed on 

 one side or the other to expose the bones, and between them, in a 

 few places, to show the skin of the under side of the body, which 

 in some places lies in juxtaposition with that of the upper side, 

 in others separated by a thin layer of the matrix. 



A dermal covering of peculiar type in Trimerorhachis has been 

 several times observed by Cope, Case, and myself, but it was 

 assumed that it covered the ventral region only, and its nature 

 was ill understood. The present specimens show very conspicu- 

 ously that it covered the whole body, with the exceptions men- 

 tioned; in the preparation of the skull not a trace of it was seen, 

 but it is closely connected with its hind margins. In no place in 

 these specimens does it appear to have been more than a milli- 

 meter in thickness. It is composed of slender and delicate bony 

 nbrillae, in short pieces, and apparently in several layers. In 

 another specimen (Fig. 3, B, C,) transverse sections show that the 

 bony rods were in numerous layers. As these nbrillae He in this 

 specimen they extend through a thickness of 6 or 8 mm., and are 

 separated from each other by intervals greater than their own thick- 

 ness. It seems hardly possible that postmortem causes could have 

 separated them so uniformly, and one must conclude that they were 

 imbedded in a considerable thickness of integument, at least a fourth 

 of an inch. How long any of the rods were I cannot say; the longest 

 connected piece that I trace is scarcely a fourth of an inch. It is 

 still possible that the sections represent the ventral skin, since 

 nothing of their character is visible in the connected skeleton. 



Notwithstanding this thickness, the skin must have been 

 flexible to have followed every inequality of the bones below it. 

 It was doubtless covered by a smooth epidermis. 



