328 A. JE. Verrill — JVbrth American OpJduroidea. 



0. hirsuta (Lym.) Ver. Disk-spines slender, tapered, acute. 

 Arm-spines five or six, strongly serrate ou the edges. Three tootli- 

 papillse. Two flat tentacle-scales. 



0. ensifera Ver. Disk-scales visible, bearing small conical 

 spinules. Spines four, blunt, mostly flat. Two flat tentacle-scales 

 on the basal joints. 



0. cervicornis (Jjjra.) Ver. Disk with granules and small acute 

 spinules. Tentacle-scales two, spiniform ; pores very large, open. 

 Arm-spines six, short, flat, serrate. 



qq. — Ophiotreta Ver., lS99a, p. 40. Only one or two, rai'ely three, 

 oral tentacle papillae, which are flat. Two to four or more 

 tooth-papillae. Arm-spines terete or only a little flattened, 

 slender, serrulate or nearly smooth. 



0. lineoluta (Lym.) Ver. Arm-spines six or seven, slender, nearly 

 smooth. Tooth-papillse three to five. Two unequal tentacle-scales 

 on several basal joints. Disk evenly granulated, and with a few 

 scattered spines. Jaws often bear granules. 



0. sertata (Lym.) Ver. Tooth-papillae two or three. Spines 

 seven, finely serrulate, partly flattened. 



DD. — Ophiothamnus Lym. Adoral shields large, wedge-shaped 

 with the broad distal end separating the narrow ovate oral 

 shield from the side arm-plate. Disk-scales exposed. 

 Radial shields more or less naked, close together. 



*0. gracilis Ver. Arm-spines four or five, upper ones slender, 

 lowest rough. Disk with truncate,, thorny stumps. Tentacle-scale 

 spiniform or palmate. 



0. vicarinsJjjjn. Disk-scales bear slender, tapered, acute spinules. 

 Tentacle-scale small, conical. 



0. exigua (Lym.) 



Opliiacantha should be restricted and subdivided. 



In this group the armature of the disk does not seem to be cor- 

 related with other important characters ; neither does the number 

 nor the length of the arm-spines, nor their solidit}^ or translucency, 

 or hollowness, nor their degrees of roughness. 



One of the characters that seems to be of much importance for the 

 separation of the typical genus, from other allied generic groups, 



