A. JE. Yerrill — North Americayi Ophiuroidea. 335 



a. — Spines slender, tajjered, terete, or bxit little flattened ; often 

 nearly smooth, or only microscopically serrulate ; rougher 

 when young, 



h. — Basal rows of spines approximate dorsally on the first or 

 second joint. 



c. — One odd tooth-papilla. 



O. vepratica Lym. Arm-spines eight, long and tapered. 



0. segesta Lym., "78. Disk-spines slender, mixed with thorny 

 stumps. 



*0. Bairdii Lym., '83. Disk with granules and some tapered 

 spines. Jaws granulated more or less. 



*0. hidentata (Retz.). Spines somewhat rough or serrulate, espec- 

 ially when young. Disk-spinules are small, thick, rough, obtuse 

 stumps. 



* 0. ahyssicola Sars. Disk-spinules minute. 



* 0. acideata Ver., '85. Spines eight or nine, tapered, ujjper ones 

 nearly smooth. Disk-spinules with three to five sharp points. 



*0. cmomala Sars.f Spines eight or nine, all terete, tapered, finely 

 serrulate; six arms. 



* 0. enopla Ver., '85. Spines four or five, serrulate ; outer oral 

 papillae clustered. 



cc. — Two or three tooth-papillae. Distal oral papillae or oral 

 tentacle-scales clustered. 



* 0. spectabilis Sars. Disk-spinules large, tapered, acute. 



hh. — Basal rows of spines not very closely approximate doi-sally. 

 d. — Dorsal arm-plates, at base of arras, separated by side plates, 

 or only slightly in contact. 



* 0. fraterna Ver., '85. Disk covered with minute spinules having 

 three to five sharp points. 



* 0. crassidens Ver., '85. Disk with small tapered spines. Oral 

 papillae very stout. 



0. Bartletti Lym., '83. [Ophiopora Ver., p. 345.) No tentacle- 

 scales. 



dd. — Dorsal arm-plates, at base of arms, distinctly joined. 

 e. — Disk and radial shields covered with spinules, or mixed spines 

 and granules. 



f This species is viviparous. One specimen from off Nova Scotia has several 

 six-armed young clinging about the mouth and genital slits. 



