A. E. Verrill — JVorth American OpMuroidea. 323 



vary. These ophiurans are able not only to reproduce a wliole set 

 of arms, but the entire upper part of the disk itself may be lost and 

 reproduced. 



As for the species included in the following tables, I have person- 

 ally studied nearly all of them, and the few that I have not seen are 

 well figured by Mr. Lyman. 



Dichotomoiis analytical table of the East Coast and West Indian 

 species that have been referred to Ophiacantha {sens, ext.) 



In this table I have arranged the species as nearly as possible in 

 accordance with what seems to be their natural relations. 



Those prefixed by an asterisk (*) are from the American coast 

 north of Cape Hatteras. All others are from the West Indian fauna. 



A. — Oral shields join the first side arm-plates. Adoral shields 



are entirely proximal to the oral shields. 

 B. — True Ophiacantha. Disk wholly, and radial shields mostly, 

 covered with small crotchets, thorny stumps, or short spin- 

 ules or granules, or with a mixture of these forms. 

 C. — Disk covered with small crotchets, or short thorny stumps, or 

 short spinules, with no elongated spines nor granules. 

 d. — Arm-spines finely serrulated, or nearly smooth under a simple 



lens, usually long and tapered, hollow, not glassy. 

 e. — Opposite basal rows of arm-spines, in the adults, are closely 



approximate dorsally or nearly so. 

 f. — Oral papillte form a simple row, the distal one being gener- 

 ally the largest. 



* 0. bidentata (Retz.). Disk with short, thick, rough, obtuse stumps 

 and crotchets. Distal oral papilla? wider, truncate. Tentacle-scale 

 single, obtuse. 



* 0. aculeata Ver. Disk with slender, thorny, stumps. Distal 

 oral papilla wide, flat, mucronate at the corner. Spines eight or 

 nine, nearly smooth. Tentacle-scale lanceolate, acute. Arm-spines 

 not always approximate dorsally. 



each side, not movable. The large outer tentacle-pore is visible from below, 

 when the distal papilla is removed. The first oral tentacle is far up in the distal 

 part of the slit and has no papillse. The uppermost tooth is longer and more 

 pointed than the rest. There may be two clavate tentacle-scales on the first 

 joint. 



