330 A. E. Verrill — JVbrth American Ophiuroidea. 



Series I. 

 Ophiacantha (restricted). Types, 0. setosa and O. bidentata. 

 Group A. — Typical Ophiacantha. 



Oral papillse form a simple row. One median tooth-papilla at the 

 tip of the jaw. No special oral tentacle-scales at the distal angles 

 of the mouth-slits, though the outer papilla, which serves as a ten- 

 tacle-scale, may be wider than the rest. Oral tentacle-pore not 

 exposed outside of the jaw-margin. Disk-scales more or less ob- 

 scured by integument and bearing spinules, thorny stumps, crotchets, 

 or granules. Radial shields rather narrow, separated more or less, 

 mostly concealed by cuticle. Arm-spines usually long and slender, 

 unequal, more or less rough, often glassy or translucent, often hol- 

 low. Dorsal arm-plates usually all separated by the side arm-plates; 

 sometimes, on a few basal joints, they are slightly in contact. 



To this section a large majoritj^ of all the described species belong. 



Group B. — Ophientodia Ver., 1899a, p. 41. 



Two, three or four tooth-papillje clustered at the tip of the jaws. 

 Otherwise nearly as in section A. Distal oral papillae not clustered. 



The published figures of several species shows two paired papillae, 

 directed centrally, at the tip of the jaws. They may not always 

 stand on the dental plate and in such cases should be counted as oral 

 papillge, but in some cases they have been determined as true tooth- 

 papillie. Probably in this section there may be a central tooth- 

 papilla that has been overlooked in some species, by reason of its 

 position, high up on the jaw, or its smaller size. In some cases it 

 may have been accidentally lost. But in some specimens either two 

 or three papilla? occur on different jaws. Therefore, I consider the 

 presence of three tooth-papillse as the usual character of this division. 

 The species need revision as to the tooth-papillae. (See also group 

 VII, page 338.) 



a.— Radial shields rather small, narrow, mostly concealed. 



0. scutata Lym. Three tooth-papillae ; eight to ten thorny arm- 

 spines. Radial shields long and narrow, sometimes naked. 



O. cuspidata Lym. Three tooth-papilla\ 



0. pectinxda Ver. Three or four tooth-papilla?. Dorsal arm-plates 

 pectinate on the outer edge. 



