A. E. Verrill — North American Ophiuroidea. 329 



hitherto confounded with it, is the nature of the adoral shields. In 

 the typical group these are small and quite in front of the oral 

 shields. In several other divisions they extend outward in a distal 

 lobe that separates the oral shield from the side arm-plates, as in 

 Ophiocopa^ etc. (See group AA, p. 327, and group XIII, p. 340.) 



Other characters of importance for the separation of groups of 

 some value, are the presence of several tooth-papillae at the apex of 

 the jaw (groups B, C, G, K, pp. 330-333); the presence of a large sub- 

 marginal oral tentacle-pore, with special papillae around it, in a row 

 or cluster (see group J, p. 333); the partial nakedness of the disk- 

 scales and radial shields (group F, p. 332) ; the size and contiguitj^ of 

 the radial shields (group G, p. 332); the contiguity of the dorsal arm- 

 plates (group G, p. 332); absence of tentacle-scales and the large size 

 of part or all of the pores (group H, p. 333, and group E, p. 332). 



Some of these characters, even those of most importance, have 

 not been referred to in many of the published descriptions, nor repre- 

 sented in the figures. Therefore many of the species cannot, at 

 present, be definitely classified. Mr. Lyman's figures, in the 

 Voyage of the Challenger, are generally very accurate, but even some 

 of these fail to show certain details of structure needful for accurate 

 classification of the species of this genus. 



Ophioraitra Lyman (typical group) differs but little from some 

 sections of Ophiacantha. It has the tooth-papillae and distal oral 

 papillae numerous and clustered, as in section C ; the distal oral ten- 

 tacle-pore is large and partly exposed, as in section J. The radial 

 shields are large and nearly naked and the disk scales are visible 

 and spinose. Several species referred to Ophiacantha by Lyman 

 also have naked disk-scales and radial shields (groups F and B, aa). 



Subdivisions of Ophiacantha. 



From the preceding remarks and table, it will be plain that several 

 genera and subgenera* may be separated from the old genus Ophia- 

 cantha with characters that appear to be of as great morphological 

 value as those that characterize, for instance, Ophiomitra or Ophio- 

 chiton. 



* Most of these subdivisions wei'e pi'oposed in the Report on the Ophiuroidea 

 of the Bahama Exped., Nat. Hist. Bull., Univ. Iowa, v, 1899. (Designated as 

 1899a in this article.) 



