BULLETIN OF THE 
Ophiacantha cosmica sp. nov. 
Plate X. Figs. 251 - 254, 262 - 265, 269, 270. 
Special Marks, — Eight or more feebly thorny arm-spines. Side arm-plates 
only moderately prominent. Disk crochets rather coarse. 
Description of an Individual (Station 157). — Diameter of disk 18 mm. 
Length of arm 100 mm. Width of arm without spines 4 mm. Seven mouth- 
papille to each angle, whereof the innermost is broad and flat, like the teeth ; 
the others are short, pointed, and very stout ; outside these, and a little higher 
in mouth-slit, is often a rounded scale of the second mouth-tentacle. Besides 
these, there are, on the mouth-frames, from two to four small, peg-like papilla. 
Mouth-shields wide heart-shape, with angle inward ; length to breadth 2 : 3.5. 
Side mouth-shields rather narrow, somewhat curved, meeting within, closely 
joined to surrounding parts. Under arm-plates wide pentagonal, with outer 
side curved, and laterals a little re-enteringly curved. Upper arm-plates wide 
fan-shaped, with an angle inward, which in the basal plates is truncated. Side 
arm-plates stout and moderately prominent ; meeting below, near base of arm, 
but not above. Towards end of arm they meet above and below, and are more 
prominent, so as to give it a somewhat knotted look. Disk full, and rising con- 
siderably above the arms ; densely and evenly set with small stumps, which, being 
freed of skin, are seen to be composed of five or six thorns, of different lengths, 
soldered side by side ; these stumps appear also on the first two upper arm- 
plates. Radial shields and disk-scales hidden. Eight even, translucent, cylin- 
drical arm-spines, which taper to a blunt point and are under the microscope 
slightly rough but not thorny ; lengths to that of an arm-joint 3.5, 3.5, 2.8, 
2.5, 2.5, 2.2, 2, 2 :1.5. Tentacle-scales rather small, longer than broad, 
pointed. Color in alcohol, straw. 
The specimen just described is unusually large for this division of the genus, 
which leads one to think that the bulk of those now known are immature, and 
therefore to be treated with all the more caution. The young of Ophiacantha 
differs from the adult as follows: 1. the arm-spines are fewer, longer, and more 
slender and thorny ; 2. the side arm-plates are much larger and more project- 
ing, giving a strongly knotted or beaded look to the arm ; 3. the mouth-papille 
are often less numerous and more slender ; 4. the armature of the disk is more 
delicate, and the stumps or spines more thorny. Thus, a younger specimen 
from the same station had a disk of 6 mm. in diameter and ‘an arm 33 mm. 
long. There were seven slender arm-spines, the upper ones much the longest, 
and bearing fine thorns on the lower part of the shaft ; the arms were decidedly 
knotted, though not so much so as in some other species (e. g. O. serrata). The 
disk-stumps had a,short trunk which supported a crown of four or five thorns, 
and resembled Fig. 285, of Plate X. 
Another specimen (Station 122) was a little larger than the foregoing, and re- 
sembled it. There were eight scarcely thorny arm-spines, the three uppermost 
much the longest, 3.3:mm. (Pl. X. Fig. 262). The disk was closely and evenly 
