158 NATURAL HISTORY BULLETIN 



the narrow paxillar area, or wider, compactly granulated. In- 

 feromarginal spines two, small, slender, acute; lower side of 

 plates covered with short, flat spinules, and with an aboral series 

 of small spines. Adambulacral spines small, triseriate. 



A. cingulatus Sladen. 

 AA. Adambulacral spines of second row not notably en- 

 larged, nor very unequal; all rather slender; one sometimes 

 longer. 



I. Superomarginal plates have a row of small spines, at least 

 proximally, in adult. 



J. Adambulacral spines few and slender; superomarginal 

 spines confined to the proximal plates; outer surface of plates 

 granulated. A. alligator Perrier. 



JJ. Adambulacral spines triseriate, in three regular rows of 

 three each ; all slender ; outer ones very slender. Superomar- 

 ginal spines form a continuous row to tip of rays, slender, acute ; 

 the plates are narrow and high, covered with elongated granules 

 or short spinules. Inferomarginal plates project beyond the 

 upper ones ; the two marginal spines are slender, acute ; lower 

 surface covered with small spines of various sizes, not limited to 

 two rows, and with small acute spinules between them. 



A. nuttingi Ver., nov. 



II. Superomarginal plates are destitute of spines or tubercles. 

 Dorsal paxillge form transverse rows on the rays: Inner adam- 

 bulacral spines slender, three distally, often four proximally. 

 Pedicellariae often present. 



K. Superomarginal plates transversely convex and closely 

 granulated. Dorsal paxillse form transverse rows and have short 

 capitate or clavate stellate spinules. Inferomarginal plates have 

 two slender, acute spines, or often three proximally; lower sur- 

 face with two irregular rows of small acute spines and covered 

 with minute, slender, acute spinules. 



L. Adambulacral plates have proximally three to five rather 

 long, slender spines in inner series ; three to five more slender in 

 a row in second series ; and usually three or four still more slen- 

 der in outer series. Few or no pedicellariae on adambulacral 

 plates. A. mtidus Verrill, nov. Typical. 



LL. Adambulacral plates have, at least in part, a large pedi- 

 cellaria, usually with three slender valves, on the actinal side, re- 



