MUSEUM OF COMPARATIVE ZOOLOGY, 135 
one large and rounded, and one smaller and narrower. Color in alcohol, 
white, 
A smaller specimen (Station 24) was more evenly granulated, and the radial 
shields were quite hidden. The upper arm-plates were so thin as to show the 
arm-bones through. 
Station 24, 390 fathoms, 3 specimens, Station 33, off Bermuda, 300 fathoms, 
1 specimen. 
The following four genera are allied. Ophiacantha is distinguished by the 
delicate scales and slender radial shields obscured by skin ; Ophiothamnus, by 
its wide naked radial shields, and by the peculiar jaw-cover of three symmetrical 
pieces ; Ophiomitra by the coarse disk-plates and scales, and wide naked radial 
shields ; and Ophiocamax by the tufts of numerous spiniform mouth and tooth- 
papilla, and the scales of the mouth-tentacles borne on a special plate. The 
old genus Ophiacantha embraces the greatest variety of forms, from O. bidentata 
and 0, vivipara, which come near Ophiocoma, to the delicate O, pentacrinus, 
with its thorny, translucent arm-spines and its knotted arms. 
OPHIACANTHA Mixx AnD Tnoscm. 
Disk covered by small delicate scales, and long narrow radial shields, the 
whole nearly or quite obscured by a skin beset with little thorns or stumps, 
Teeth and mouth-papilla, but no tooth-papillo, Numerous arm-spines (5 — 9), 
arranged along sides of side arm-plates, which are prominent, and nearly or 
quite meet above and below. In each interbrachial space two genital openings, 
beginning just outside the mouth-shield. 
OPHIOTHAMNUS Lym. 
Disk beset with fine thorns or spines, and covered by rather large scales and 
naked radial shields. Teeth, and stout, close-set mouth-papille, but no todth- 
papilla. Numerous (8) thorny translucent arm-spines, arranged along sides of 
side arm-plates, which are prominent, and nearly or quite meet above and be- 
low. In each interbrachial space two genital openings, beginning close out- 
side the mouth-shield. The jaw-cover is in three pieces, arranged symmetrically 
like the mouth-shield and side mouth-shields, 
OPHIOMITRA Lym. 
Disk covered by large, irregular plates and scales, and wide naked radial 
shields, the whole naked and beset by thorny stumps or spines. "Teeth, and 
mouth-papille, but no tooth-papille. Numerous (5 = 7) thorny translucent 
arm-spines, arranged along sides of. side arm-plates, which are prominent, and 
nearly or quite meet above and below. In each interbrachial space two geni- 
tal openings, beginning close outside the mouth-shield. 
