A. K Verrill — North American Ophiuroidea. 337 



0. sertata. Small, pear-seed-shaped. 



O. scutata. Long and narrow. 



0. ensifera. Small, nari'ow, usually largely covered. (See 

 Ophiopristis, p. 347.) 



0. Ntcttingii. Crescent-shaped, narrow. (See Ophialc(xa, p. 331.) 



Several other species are apt to have the distal end of the radial 

 shields more or less exposed. In many cases the covering is probably 

 accidentally rubbed off. 



IV. 



Dorsal arm-plates, on basal part of arms, in contact, not separated 

 by the side-plates. 



a. — Dorsal arm-plates rather narrow. 



0. llneolata. Ventral plates slightly separated. (See Ophio- 

 treta, pp. 333, 347.) 



aa. — Dorsal arm-plates broad. 

 b. — Dorsal plates extensively joined. (See Ophiacanthella, p. 344.) 



0. Nuttlngii. Ventral plates in contact. 

 0. Troscheli. Ventral plates separated. 



hb. — Dorsal plates little joined. 



0. cosniica. Ventral plates separated. 

 0. mixta. (See p. 346.) 



Tentacle-pores all unusually large. 



O. Bartletti. No tentacle-scales. (See Ophiopora, p. 345.) 

 0. cervicornis. Two spiniform tentacle-scales. (See Ophio- 

 jjristis, pp. 333, 347.) 



VI. 



A cluster of three or more tooth-papilloe at the tip of the jaw.* 



0. lineolata (three or four tooth-papilloe). 



O. scutata (three or four, often only two visible below). 



* Several extralimital species belong to this group, such as O. Valenciennesi 

 Lym., with three tooth-papillas and one oral tentacle-scale ; O. cuspidata Lym. ; 

 O. marsiqjialis Lym.; O. rosea Lym.; the last has a cluster of tooth-papillae and 

 also several oral scales, (See p. 338, note, and p. 348.) 



