MUSEU.M OF COMPARATIVE ZOOLOGY. 121 



smooth, and tubular, with side arm-plate3 very large, and upper- and under 

 arm-plates small. Basal tentacle-pores very larj,'e ; those beyond small and 

 situated near sides of arm. An arm-comb. Atm-spines minute, and stand- 

 ing on outer edge of side arm-plate. Two long genital openings in each inter- 

 brachial space. 



This is the most singular-looking genus yet found among Ophiuridoe. With 

 its peg-like central primary plate and dome-like di.sk it suggests a simple armed 

 crinoid whose head has been broken from the stem. By its heavy, closely 

 soldered plates and peculiar tentacle-pores, it recalls Ophiomusiura ; by its 

 enclosed mouth-tentacles and arm-comb, it brings to mind the deep-sea 

 OiMoghjphce ; but it differs pretty widely from both. 



Ophiopyrgus Wyville Thomsoni sp. nov. 



Plate V. Figs. 135 - 137. 



Special Maries. — One minute arm-spine on basal joint ; farther out, none ; 

 a double arm-comb over top of arm, the upper one consisting of three or four 

 small papilla) on edge of outer end of genital scale ; the under, likewise of 

 three or four papillae, on edge of side arm-plate. Interbrachial space below 

 wholly filled by mouth-shield. 



Description of qn Individual (Station 172). — Diameter of disk, 4 mm. 

 Height of disk 4.3 mm. Length of arm 13 mm. Width of arm 1.2 mm. 

 Mouth-papilla; small, similar, separated, tooth-like ; seven or nine to each angle, 

 whereof the innermost is slightly largest. Mouth-shields longer than broad, 

 oval, with a peak inward, occupying the entire interbrachial space below, and 

 bending upwards to half the height of the arm. Side mouth-shields very small 

 and sunken, meeting within, and covering only the inner peak of mouth- 

 shield. First under arm-plate very long axe-shape, with a curs'ed edge out- 

 ward and a long, tapering point inward, compressed between two large oval 

 tentacle-pores ; second plate similar, but smaller ; third and fourth plates 

 shorter and still smaller ; beyond which the plates are represented by a small 

 knot of a transverse diamond-shape, and growing rapidly less towards end of 

 arm. Side arm-plates large, but not swollen, meeting widely above and be- 

 low, occupying most of the arm, which acquires thereby a tubular, rapidly 

 tapering form. The side arm-plates belonging to second under plate are wide, 

 and stretch laterally to meet the mouth-shield. Disk as high as wide, rising 

 in a steep dome surmounted by a sugar-loaf projection, which is the central 

 primary plate, and is surrounded by five other primaries, longer than broad, 

 and hexagonal, outside which are small, angular, radial shields, which are 

 joined ; in the interbrachial space are one pentagonal and one rounded hex- 

 agonal plate, the latter joiiung the upper edge of the mouth-shield ; all the 

 plates are closely soldered, slightly swollen, and, as well as the arm-plates, are 

 microscopically tuberculous. Genital openings long, curved and narrow, extend- 

 ing from inner point of mouth-shield to a point over arm. One minute peg- 



