148 BULLETIN OF THE 
den. Seven long, slender, translucent arm-spines, essentially smooth, only the 
lower ones being slightly rough under the microscope. Lengths to that of an 
arm-joint 3.5, 3.5, 3.5, 2.8, 1.8, 1.9, .8 : ۰ Tentacle-scales narrow and sharp. 
Color in alcohol, white. 
The great size of the side arm-plates and the number and length of the arm- 
spines mark this as an immature specimen, but the specific characters are not 
found in any other. 
Station 214, 500 fathoms, 1 specimen. 
Ophiacantha serrata sp. nov. 
Plate X. Figs. 272, 273. 
Special Marks. — Disk closely and evenly set with minute grain-like stumps 
bearing a crown of blunt thorns ; arm-spines long, slender, strongly thorny, 
translucent, mounted on steep, narrow, much projeeting side arm-plates. 
Description of an Individual (Station 219). — Diameter of disk 6 mm. Length 
of arm about 32 mm. Width of arm without spines 1.8 mm. Seven flat, 
rather blunt mouth-papilla, not crowded ; the innermost one much larger and 
squarish ; besides these, the first, under arm-plate bears two tentacle-scales, one 
to each of second pair of mouth-tentacles. Four flat teeth, similar in shape 
to the innermost mouth-papilla. Month-shiehls much wider than long, of a 
transverse diamond-shape, with lobe-like angles, Side mouth-shields straight 
and narrow, nearly or quite meeting within. First under arm-plate small and 
rounded, and bearing on its inner edge two tentacle-scales ; second. plate long 
axe-shaped, with a curve without, a well-marked angle within, and lateral 
sides re-enteringly curved ; third plate proportionately shorter and with the 
inner side a very obtuse angle. Upper arm-plates small, of a wide fan-shape, 
with the angle inward. Side arm-plates large, meeting widely above and be- 
low, rising very suddenly to form a high, narrow spine-ridge, 0 that the arm. 
has the look of a series of short cylinders alternating with burrs (Fig. 272). Disk 
densely and evenly beset with minute grain-like stumps, bearing a crown of 
blunt thorns (Fig. 273). Scaling and "dial shields covered, except outer tips 
of the latter, Nine long, slender, translucent, strongly thorny arm-spines ; 
lengths to that of an arm-joint 4, 4, 4, 3.2, 2,7, 2.6, 1,8, 1,8, 19 1T. One small 
spiniform tentacle-scale. Color in alcohol, white mottled with pale brown. 
The small number of teeth and large side arm-plates show the specimen to 
be young, but the specific marks are good, and would be carried forward to the 
adult, which doubtless has ten or a dozen long, glassy, thorny arm-spines, with 
side arm-plates not so exaggerated in their projection. 
Station 219, 152 fathoms, 1 specimen. 
