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 tlie 

 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 Ly 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 0. hidentata 

 and 0. vivipara, which come near Ophiocoma, to the delicate 0. pentacrimis, 

 with its thorny, translucent arm-spines and its knotted arms. 



OPHIACANTHA Mull and Trosch. 



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-papillaj, but no tooth-papillse. 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 Ltm. 



Disk beset with fine thorns or spines, and covered by rather large scales and 

 naked radial shields. Teeth, and stout, close-set mouth-papilla;, but no tooth- 

 papillae. 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 Ltm. 



Disk covered by large, in-egular plates and scales, and wide naked radial 

 shields, the whole naked and beset by thorny stumps or spines. Teeth, and 

 mouth-papillae, but no tooth-papillae. 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. 



