A. E. Verrill — North American Ophiuroidea. 351 



* 0. spinea Ver. Oral papillae not very numerous distally. Disk- 

 scales small, with small conical spinules. Arm-spines eight or nine, 

 rough, hollow, the rows not approximate dorsally. One or two 

 tentacle-scales. 



AA. — Op)hioplinthaca, gen. nov. Type, 0. dipsacos Lym. One odd 

 tooth-papilla, oral papillfe in a nearly simple series, not 

 clustered distally. Interradial margins of disk notched or 

 deeply emarginate. Marginal and submarginal disk-scales 

 large and specialized. Arm-spines thorny and glassy, 

 usually hollow. Radial shields large and broad^ naked or 

 nearly so. First tentacle-pore decidedly larger, with two 

 or more scales. Oral shield joins the first side arm-plates. 



B. — Radial shields in contact along most of their length. Rows of 

 spines not approximate dorsally. 



c. — Upper arm-plates distinctly separated by the side plates. 



0. dipsacos (Lym.). Arm-spines six, hollow, very thorny, the two 

 upper ones very long. First tentacle-pore with two scales. 



ec. — Upper arm-plates on basal joints slightly joined, or barely 

 separate. Two or more distal oral tentacle-scales, similar 

 to other oral papillae. 



0. incisa (Lym.). Arm-spines five or six, flattened, thorny on 

 edges. Three to six tentacle-scales at first pore, one or two farther 

 out. Disk-scales with few, nearly smooth, conical spinules. 



BB. — Radial shields not in contact, or only slightly so distally. 

 Spines glassy and thorny, the rows not approximate dorsally. 



d. — Radial shields in contact at the distal ends, very large and 

 wide. 



e. — Upper arm-plates separated. 



0. cardtiiis (Lym.). Spines six, very thorny. Disk-scales with 

 thorny stumps, marginal scales very large. Tentacle-scale one, 

 lobate. 



ee. — Upper arm-plates, on basal joints, not separated by side 

 plates. First tentacle-pore larger, with two or three scales. 

 A flat oral tentacle-scale. 



0. plicata (Lym.). Radial shields joined distally in young; sepa- 

 rate in adult. Disk-scales with small, conical spinules. Arm-spines 



