MUSEUM OF COMPARATIVE ZOOLOGY, 121 
smooth, and tubular, with side arm-plates very large, and upper and under 
arm-plates small. Basal tentacle-pores very large ; those beyond small and 
situated near sides of arm. An arm-comb. Arm-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 Ophiuride. With 
its peg-like central primary plate and dome-like disk 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 Ophiomusium; by its 
enclosed mouth-tentacles and arm-comb, it brings to mind the deep-sea 
Ophioglyphe ; but it differs pretty widely from both, 
Ophiopyrgus Wyville Thomsoni sp. nov. 
Plate V. Figs. lov - 137. 
Special Marks, — 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 papilla, on edge of side arm-plate. Interbrachial space below 
wholly filled by mouth-shield. 
Description of an 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, oceupying 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 curved edge out- 
rard 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 joining 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- 
