326 A. E. Verrill — North American Ophiuroidea. 



O. vepratica Lym, Arm-spines eight, long, tapered. Oral papillae 

 three, conical. Tentacle-scale single, large, conical or sj^iniform. 



II. — Disk-spines elongated, mixed with crotchets or thorny stumps. 

 Arm-spines more or less finely serrulate. 



O.varispinaYew Arm-spines eight, serrulate, translucent. Disk 

 with thorny stumps and few acute spines. Tentacle-scale single, 

 flat, subspatulate. Oral papillae wide, flat, obtuse; distally there is 

 often an extra marginal one. 



hh. — Disk covered with small close granules alone. Basal rows of 

 spines not approximate dorsall3^ Arm-spines serrulate ; 

 under arm-plates short and broad, separated. 



* 0. graniiUfera Ver. Arm-sj^ines nine, the upper ones long and 

 slender, finely serrulate, lower ones short, rough. Oral papillae all 

 spiniform. Tentacle-scale lanceolate, two on first joints. 



BB. — Radial shields largely uncovered. Disk-scales either jjartially 

 naked and easily visible, but bearing more or less granules 

 or spinules, or else entirely concealed, 

 m. — Disk-scales largely exposed. 



n. — Ophialccea Ver., 1899a, pp. 38, 42. Dorsal arm-plates largely 

 in contact. Arm-spines nearly smooth, the rows widely 

 separated dorsally. 



0. Nnttingii Ver. Arm-spines four, short, tapered. Disk-scales 

 small, exposed, bearing small spinules. Radial shields partly 

 exposed, narrow, separated. Tentacle-scales single, large. 



nn. — Ophiomitrella Ver., 1899a, pp. 39, 43. Dorsal arm-plates 

 separated by the side-plates. Arm-spines slender, thorny; 

 the basal rows approximate dorsally. 



0. Icevij^ellis (Lym.) Disk-scales small, sometimes entirely naked, 

 sometimes with small scattered granules. Radial shields small, sep- 

 arate, partly naked. Tentacle-scale single, small, acute. A pair of 

 papillae on the first under arm-plate. 



mm. — Disk-scales mostly concealed, but radial shields naked. 



o. — Ophiacanthella Ver., 1899a, p. 39. Basal rows of spines not 

 approximate dorsally. Dorsal arm-plates largely in coji- 

 tact. Radial shields long, mostly naked, in contact by their 

 edges. Arm-spines nearly smooth. Three tooth-papillae. 

 Oral papillae four, conical, all similar. 



