MUSEUM OF COMPAKATIVE ZOOLOGY. 47 



that of an under arm-plate, .2, .3, .3, .3, .5, .7, .8, 1, 1.2, .7, .7 : .7. The basal 

 under arm-plates, as far as the fifth or sixth, bear on each lateral side three 

 long, flat, spatula-like tentacle-scales, which project over the pore; for some 

 distance beyond there are but two such scales, while a third, trowel-shaped, 

 stands on the edge of the side arm-plate. One third out on the arm there re- 

 mains only the large trowel-shaped scale. Color in alcohol, pale gray. 



Station, off Tristan d'Acunha, 1000 fathoms, 2 specimens. 

 ' The peculiar twisting upward of the arms and disk of Ophiomyces is explained 

 by the absence of radial shields, a want not yet observed in any other genus. It 

 seems, then, that one function of radial shields is to keep the disk in shape, 

 somewhat like the action of the sticks of an umbrella. 



Ophiomyces spathifer. 



Plate XIV. Figs. 386 - 388". 



Special Marks. — Outer mouth-papillae large and paddle-shaped. One flat, 

 rounded tentacle-scale. Ten flattened arm-spines of various shapes, whereof 

 the two lowest are borne on the under arm-plate. 



Description of an Individual (Station 235). — Diameter of disk 3.5 mm. 

 Width of arm next disk 1.2 mm. Three short, narrow, slightly flattened, peg- 

 like teeth, carried on a thick, lumpy jaw-plate, which also bears two long, flat, 

 narrow, spatula-like tooth -papillae. On either side of the mouth-angle are two 

 radiating rows, each of about six long, flattened papillae, which are imbricated 

 and point downward and outward, so that the entire mouth-angle is hidden by 

 them ; the inner ones are narrow and spatula-like, but outwards they grow 

 rapidly larger, so that the outermost are wide paddle-shaped, or even fan-shaped, 

 their length to extreme breadth being .7 : .5. Mouth-shields shaped like a long, 

 sharp, narrow lance-head. Side mouth-shields three-sided, delicate, separated 

 as by a wedge by the mouth-shield, which extends inward considerably beyond 

 them. Within, and indistinctly separated from the side mouth-shields, project 

 the long jaws. These parts are all hidden, and can be seen only by cutting away 

 the mouth-papillae. Under arm-plates small, with re-enteringly curved lateral 

 sides, wider without, where they are a little swollen, than within, separated by 

 the side arm-plates, which meet narrowly both above and below, and are highest 

 and most flaring at their outer edge. Upper arm-plates minute (sometimes 

 appareiitly wanting), twice as long as broad, and appearing like little swellings 

 just outside the juncture of the side arm-plates. The larger part of upper sur- 

 face of arm is thus left uncovered, so that the arm-bones and their muscular 

 bundles may be seen. Disk (as usual in the genus) distorted and pushed up- 

 ward, covered uniformly with minute, thin, translucent, flat scales, without 

 spines; there are about 13 in the length of 1 mm. Ten arm-spines, of which the 

 three highest are equal, slender, narrow and tapering, and as long as any ; the 

 next two are of about the same length, but broad and flat, with rounded ends ; 

 the next three similar, but shorter ; the two lowest spatula-like, with ends cut 

 square off, and carried, not on the side arm-plate, but widely spaced on the 



