MUSEUM OF COMPARATIVE ZOOLOGY. 129 
OPHIOTROCHUS * gen. nov. 
Disk flat and round, covered with thin, more or less granulated scales, and 
naked radial shields. Arms slender, tubular, each joint constricted at its base ; 
side arm-plates meeting widely above and below ; upper arm-plates rudimen- 
tary. Scale of second pair of mouth-tentacles lying between side mouth-shield 
and outer mouth-papille. There are teeth and mouth-papille ; no tooth- 
papilla. Smooth arm-spines on outer edges of side arm-plates. 
Ophiotrochus panniculus sp. nov. 
Plate VI. Figs. 158 - 160. 
Special Marks. — First arm-joint, outside of disk, much wider than those be- 
yond, and. bearing four slender spines ; the others having only two. A sparse 
granulation on the lower interbrachial space. 
Description of an Individual (Station 218). — Diameter of disk 6 mm. 
Length of arm 26 mm. Width of arm without spines .8 mm. Two wide, very 
short, close-set mouth-papilla, occupying the whole of each side of an angle; 
and at the apex three more, very small, short, and spiniform. Mouth-shields 
three-sided, with a long angle inward, and outer corners slightly rounded ; 
length to breadth 1.3: 1. Side mouth-shields much longer than broad, 
swelled without like a knob, long and very narrow within, where they nearly 
or quite meet; they usually bear a few grains, First under arm-plate small 
and rounded, with a slight peak inward ; the rest are somewhat broader than 
long, pentagonal, with an angle inward, the outer edge rounded, and re-entering 
curves on the lateral sides, Side arm-plates making together a tubular figure, 
flaring outward, meeting broadly below and above, Upper arm-plates very 
minute, and almost disappearing towards middle of arm, situated at the outer 
junetion of the side arm-plates, three-sided, and with a peak within. Disk flat 
and round, covered with thin delicate seales ; six rounded primary plates, sepa- 
rated by a line of scales, may be distinguished in the centre; the rest are more 
or less angular, and irregularly disposed. Radial shields broader than long, of 
irregular shape, with rounded angles, narrowly separated by a single line of 
scales, Interbrachial space below covered with thin scales sparsely set with 
small grains, which stand also on the margin. Two large genital openings, 
extending from the outer corners of mouth-shield to margin of disk. On first 
joint, outside disk, four sharp slender arm-spines, placed high on side arm- 
plate, the uppermost one as long as an arm-joint, the others progressively 
shorter ; on joints beyond there are only two short spines, One large rounded 
tentacle-scale on the inner edge of each tentacle-pore ; the second pair of 
mouth-tentacles have a wide flap-like scale hinged on the side mouth-shield, 
* vis, snake ; rpoxós, wheel. 
