334 A. M Yerrill— North American Ophiuroidea. 



may be so in some cases, but mei'ely as aides for the comparison of 

 the species. They may be considered as morphological tables. The 

 genus in these XIII groups is taken as in Mr. Lyman's works. 

 For the natural subdivisions, see pages 329-333, 



I. 



Arm-spines long, thorny or prickly, more or less glassy. 



a. — Rows of spines approximate dorsally on first or second joint 



beyond disk. 

 h. — Radial shields covered ; disk spinulose. 



0. aspera Lym., '78. Arm-spines ten, slender, very thoriJ3\ 



0. pentacriniis Liitk. Spines nine or ten, long, very slender, 

 slightly thorny. 



O. pectinida Ver., sp. nov. Spines ten or eleven, very slender and 

 glassy. Tooth-papillje two to four. A cluster of oral tentacle-papillae. 



*0. tnillespina Ver., '79. Spines ten. Disk spinules slender, with 

 three or four long sharp branches. 



*0. gracilis Ver.,f '85. Spines four to six, short, except the upper 

 basals ; lower ones thorny. Disk-scales naked, with hour-glass 

 shaped, thorny stumps. 



* 0. varispina Ver., '85. Spines eight, little rough, glassy. 



bh. — Radial shields largely exposed. 



0. loevipellis Lym., '83. Spines seven or eight, little flat; naked 

 disk-scales. 



0. ecJiinulata Lym., '78. Spines nine or ten, long ; disk spinose. 

 See under Ophiotnitra. 



aa. — Basal rows of spines not closely approximated dorsally. 



0. stellata Lym., '75. Arm-spines seven, very thorny. 

 0. scutata Lym., '78. Spines nine or ten, slightly thorny. 



* 0. gramdifera Ver., '85. Spines eight or nine, part of them 

 slightly thorny. 



n. 



Arm-spines, in the adult, not distinctly thorny, but often finely 

 serrulate on the edges, especially the lower ones ; mostly rather 

 opaque, but often translucent in alcohol ; usually hollow. 



•f-TMs singular species, on reexamination, proves to belong to Ophiothamnus. 

 Its long, wedge-shaped oral shields are widely separated from the arm-plates by 

 the broad adoral shields. 



