314 



The fragment is from an intermediate position at the junetion of the root 

 and shaft, and is a little over 3 inches in length. It looks as if* when in a 

 complete condition it had been upwards of a foot in length, approximating 

 that of the dorsal spine of A. ornatissimus. Broken off at both extremities, 

 and also posteriorly, so as to leave no portion of the usual groove, it appears 

 as a solid, porous bone-fragment, triangular in transverse section toward the 

 apex, and oblong toward the root. 



The sides of the shaft are closely studded with mammillary tubercles, 

 arranged in rows directed upward and forward. The tubercles incline in the 

 same direction, and have their sides longitudinally striated. Their summits 

 are worn away, the extent of abrasion increasing, approaching the anterior 

 border of the spine. 



