MUSEUM OF COMPARATIVE ZOOLOGY. 345 



arm-spines which lie within the disk ; far out on the arm they grow some- 

 what pointed. 



Color, in alcohol, uniform pale gray. 



The chief variations noticed were in the shape of the singular outer 

 mouth-papilla;, which are sometimes more spreading in their form, or nar- 

 rower. The number of these, as well as of the inner mouth-papilla?, va- 

 ries by one or two, for each angle of the mouth. 



OfT Sand Key, Florida, in 237 to 306 fathoms. 



The specimens, many of which had cast their disks, were singularly dis- 

 torted, probably by the change of pressure from so considerable a depth. 

 The arms were twisted upwards, so that they made a parallel bunch, in the 

 midst of which was the disc, much elongated. By this torsion the mouth 

 parts were all turned outwards, and almost inverted. This singular 

 twisting is unusual. 



The species may readily be distinguished from 0. fruteclosus by the 

 fewer spines and their comparative equality. 



Ophiomyces frutectosus Lyman. 



Special Marks. — Twelve arm-spines, of which the uppermost is close to 

 the median line of the arm. The five upper ones are short and sharp ; 

 the next three long, tapering, slender ; the last four shorter, flattened, and 

 equal. 



Description of a Specimen. — Diameter of disk 7 mm. Length of arm 

 about 28 mm. The inner mouth-papilla? are rounded, stout, spiniform, 

 seven or eight in number ; they form an irregular row about the inner 

 mouth-angle, and are often turned more or less downward. The outer 

 mouth-papilla? are flattened and broad ; wider at their ends, which are cut 

 square off, than at their bases ; rudely arranged in four radiating rows, but 

 inclining downwards and outwards, and so overlapping as to cover the 

 outer part of the mouth-angle, like tiles ; there are fourteen or sixteen to 

 each mouth-angle; the longest are .7mm., and are outside. Teeth four 

 (rarely five), short, flat, stout, with a curved, cutting edge. Mouth-shields 

 very small, diamond-shaped, and almost hidden by the numerous spines 

 and papilla? about them. Side mouth-shields completely hidden by the 

 outer mouth-papilla?. Under arm-plates nearly as wide within as without ; 

 their lateral sides with a strong re-entering curve from the encroachment 

 of the large tentacle pores ; length to breadth (6th) .6 : .5. Side arm- 

 plates meeting above, but not below ; near the base of the arm they barely 

 meet above. Upper arm-plates very thin and delicate, except a median, 

 thickened crest; their outer side strongly curved, their inner side with a 

 slight peak ; they occupy only about half the width of the arm; length to 

 breadth .5: 1.2. Disk covered with fine, slightly thickened scales; about 

 44 



