38 NATURAL HISTORY BULLETIN. 



* O. sftectabilis Sars. 



j.j. — Basal rows of spines not approximate dorsally. 



k. — Arm-spines finely serrulate, not glassy. Tooth-papillae 

 single. Mouth-papillae in a simple row. 



O. segesta Lym. 



* O. crassidens Ver. 



k. k. — Arm-spines thorny and glassy. Disk-spines slender, 

 thorny, acute. Several tooth-papillae. 



O. -pectinula Ver. 



/. i. — Disk bearing few tapered spines mixed with other 

 structures. Rows of spines approximate dorsally. 



/. — Disk covered with granules, mixed with a few tapered 

 spines. Arm-spines finely serrulate or nearly smooth. 



O. veftratica Lym. 



/. /. — Disk-spines elongated, mixed with crotchets or thorny 

 stumps. Arm-spines more or less finely serrulate. 



* O. varisfiina Ver. 



h. h.— Disk covered with small close granules alone. Basal 

 rows of spines not closely approximate dorsally. Arm- 

 spines serrulate. Under arm-plates short and broad, 

 well separated. 



* O. granulifera Ver. 



B. B. — Radial shields largely uncovered. Disk-scales either 

 partially naked and easily visible, but bearing more or 

 less granules or spines, or else entirely concealed. 



m.- -Disk-scales largely exposed. 



;/. — Ophialccea V. Dorsal arm-plates largely in contact. 

 Arm-spines nearly smooth, the opposite rows widely 

 separated dorsally. 



