1024 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
visible; the latter are arranged irregularly in a circle of 6 or 7 around each paxilla. Along the margin 
of dorsal area the paxillae are arranged in definite transverse rows, but no order is distinguishable 
along the median radial line or in center of disk. 
Superomarginal plates, 33 in number (varying from 30 to 37 in different individuals) from the 
median interradial line to extremity of ray, form a well-defined, broad, and massive border to disk 
and rays. Each plate is strongly tumid along its transverse axis, so that a broad, rounded well- 
defined sulcus is formed between successive plates. The extreme tumidity of the marginal plates 
gives to this species a highly characteristic appearance. The superomarginals are longest (3.5 mm.) 
toward the base of ray — the third to twelfth plate. Breadth of fifth superomarginal 6 mm. Surface 
of plates covered with granules and delicate spinelets. Those of the transverse tumid portion are 
distinctly spaced, flat, roundish, squamiform, but not imbricating, tending to become larger on the 
abactinal surface; those covering transverse marginal regions of the plate are slender and delicate, 
giving the appearance of plush. They are longest in the bottom of the groove between the plates, 
becoming shorter toward the squamiform granules into which they pass insensibly. Under the 
microscope the latter sort are seen to be cylindrical, slightly swollen at the tips, and invested with a 
delicate membrane. 
Inferomarginal plates correspond exactly to superior series, and they encroach as much upon the 
actinal surface as do the latter upon the abactinal. They are tumid, the ridge passing obliquely from 
the middle of the superior margin toward the aboral ventral corner of plate. The upper half of this 
ridge bears a row of 4 slender, tapering, slightly flattened spines directed obliquely upward and 
outward and closely appressed to ray. The lowest but one is longest, being about one-third longer 
than its plate (except on the outer half of ray). These spines decrease in length toward the extremity 
of the ray, where the series is usually reduced to 3 with an occasional plate bearing 4. The first 5 plates 
usually bear 5, or sometimes 6 spinules. On the inner third of ray there may be 2 or even 3 short, 
more widely spaced spinules on the ventral portion of the ridge between the upper series and the 
ventral margin, situated rather toward the aboral edge of the plate. On the first 2 plates of each ray 
there is an extra spine or pair of spines on the adoral margin, on a level with the ventral series, the 
upper spine equalling the length of its plate, and in addition there is an odd spine placed close to, but 
out of line with, each of the 2 upper spines. General surface of inferomarginals is covered with 
papilliform spinelets, which become larger, flattened, and squamiform on the median tumid portion 
of the plate, and more robust toward the ventral margin. They are larger than the spinelets of the 
superomarginals. 
Adambulacral plates large and massive, about 50-54 to the ray, slightly longer than broad, and 
with a decidedly convex margin to furrow. Armature consists of a furrow, series of 11 to 13 long, 
thin, delicate, laterally-compressed spinelets, standing subparallel or diverging slightly. The outer 
spinelets are usually slightly the longest, equalling length of plate. Tips of the spinelets form a 
slightly curved border to the comb. The usual number in the furrow series is 11, decreasing at the 
tip of ray to 9, or less; covered with delicate membrane. On actinal surface of the plate are 3 irregular 
longitudinal rows of tapering, membrane-covered, pointed spinelets, there being usually 6 in the first 
series, 4 or 5 in the second, and 3 to 5 in the third, with often 2 or 3 odd very short spinelets. In 
basal portion of ray these spinelets are prominent, and are nearly as long as those of the furrow 
series; they decrease in length and number toward extremity of ray. In the first 3 or 4 plates 5 or 6 
actinal spinelets may be grouped to form, a pedicellarian apparatus. 
Mouth plates are elongate, rather narrow, and prominent actinally, the united pair being elliptical 
in outline. Their armature is somewhat peculiar, consisting of a marginal series of 9 stout, tapering 
spinelets shorter than the furrow spinelets of the adambulacrals, the median spinelets of each free 
margin being the longest of the series. About as many more smaller spinelets are continued along the 
margin adjacent to the first adambulacral. Along the margin of the median suture is a series of about 
16 stout, blunt, flattened spinelets which increase in length toward the inner extremity of the plate, 
the innermost spine being flattened, long, lanceolate, and directed with its fellow of the companion 
plate across actinostome. Between the marginal and superficial series is an intermediate series resem- 
bling the latter but with fewer spinelets. The peculiarity of the armature is that the intermediate 
and marginal series, rather closely appressed,. continue above (abactinad) the 'level of the main tooth 
along the edge of the plate, curving in such a manner as to be directed not toward actinostome, but 
across the ambulacral furrow. This double series terminates on a level with and just outside the 
