350 A. E. yerrill — North American Ophiuroidea. 



Opliiotreina of Koehler seems to be very closely related to typical 

 Ophiomitra. 



Like the latter, it has clustered tooth-j^apillae and oral papillae, 

 with a large, conspicuous distal oral tentacle-pore and special papillae 

 around it. The tentacle-pores are large and surrounded by several 

 small acute spinules. Disk-scales are small, visible, bearing acute 

 rough spinules. Radial shields are small, naked, separate, divergent. 

 Arm-spines five, serrulate. 



0. Alberti Koehl., '96, the type, is from oflf the Azores. 



Certain species referred to Ophiomitra by Koehler appear to 

 belong to Ophiomitrella. (See p. 352.) 



Synoptical table of the species that have been referred to Ophiomitra 

 (sens, ext.) and Ophiomitrella. 



Group A. — Typical Ophiomitra. 



Tooth-papillae several, clustered. Oral papilhe numerous, clus- 

 tered distally. Distal oral tentacle-pore large. Radial shields 

 large, naked, usually joined. Disk-scales visible, all of moderate 

 size, bearing stumps or spinules. Arm-spines thorny and usually 

 glassy. Two or three tentacle-scales on the basal joints, in the type. 

 Adoral shields broad, proximal to the oral shields. Interradial mar- 

 gins of disk somewhat incurved, sometimes convex, not deeply 

 notched. 



a. — Radial shields largely in contact. 



b. — Disk-scales bear short clavate or capitate stumps. Rows of 

 arm-spines not approximate dorsally. 



O. valida Lym., '69. Arm-spines nine or ten, solid, not very 

 long, roughly serrulate or thorny. 



bb. — Disk-scales bear longer and shorter, tapered, thorny spines. 

 Rows of spines approximate dorsally. 



O. ornata Ver., 1899a. This Vol., pi. xLiir, fig. 3. Arm-spines 

 long, slender, thorny. 



aa. — Radial shields divergent, in contact only distally. Arm- 

 plates separate above and below. 



number, it differs from all the species of Ophiomitra. Therefore I have referred 

 it to Ophiacantha, with which it agrees in its mouth parts. (See p. 329.) 



Another species (0. exigua Lym.) I refer to Ophiothamnus. (See p. 328.) This, 

 also, has smooth spines, and the small oral shield is separated from the side arm- 

 plates by the large adorals. 



