1032 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
Luidia hystrix, new species. 
PI. XIII, figs. 1, 2; pi. xiv, figs. 1, 2; pi. xvi, figs. 2, 2a. 
Rays 8. R = 195 mm. (longest ray, the shortest R being 178 mm.) r = 19 mm. R = 10.2 r. 
Breadth at widest part near base 20 mm. 
Rays very elongate in proportion to disk, slightly swollen above base, and thence very gradually 
tapering up to the bluntly pointed extremity; robust, depressed, with well-rounded sides. Abactinal 
surface more or less flattened on disk; convex on rays, but flattened or even slightly concave along 
median radial line. In young specimens rays are always strongly convex above. Actinal surface 
rounded, the ambulacral furrow broad and tube feet very large, with conical sucking disks. 
Paxillse of abactinal area large, crowded on disk, and there without definite arrangement. They 
are arranged in definite, spaced, longitudinal rows along rays, except in a narrow median radial area, 
where they are more crowded and not so regular. On either side of this median radial area one can 
count 6 regular longitudinal series of paxillse on the basal portion of ray and 5 over the remainder. 
Paxillse are rotund to slightly subquadrate at the margins of area. Nearly all paxillse of rays except 
the series adjacent to inferomarginal plates and those of distal portion of median radial area bear a 
robust, upright, tapering sharp thorn or spinule, about 2 to 2.4 mm. in length, placed in center of 
tabulum; those of the median radial area (proximal portion) are shorter (1.5 mm.). This spinule is 
surrounded by 5 to 8 or 10 robust, cylindrical or clavate, obtusely tipped, papilliform spinelets, 
placed also on the tabulum. External to these on the periphery of tabulum are 15 to 25 (usually 
about 17 or 18) slender .papilliform spinelets, usually somewhat irregular in thickness. Paxillse of 
the series adjacent to marginal plates are very slightly smaller than the others and lack the central 
spinule. Not infrequently paxillse of the regular spinulated series also lack the spinule, but in other 
respects they resemble the spinopaxillse. Occasionally paxillse of disk bear a short conical spinelet, 
but most of them have instead 8 or 9 cylindrical flat-topped granuliform spinelets in the center of 
tabulum, surrounded by a peripheral series of 20 to 25 much slenderer ones. 
Inferomarginal plates are very numerous, short, and wide, each with a special raised ridge, 
between which are deep fasciolar grooves. Plates bear, along the median line, a transverse series of 
4 or 5 (rarely 6) long, slightly curved, very sharp, rather delicate spines. These increase in size 
toward outer edge of plate, the inner 2 being usually much smaller than the outer 3, the median 
spine of which is longest. Toward base of ray there is less difference between the inner and outer 
spines, although the inner 2 are always much smaller. The elevation or keel of the plate, upon 
which the spines are borne, is bordered by long, slender spinelets, a few standing on the exposed 
surface, between the spines. Sides of fasciolar grooves are covered with capillary spinelets. 
Adambulacral plates are wide, but short, as seen on the actinal surface, and are united by broad 
bands of integument. The armature, which is borne on a sort of keel, consists of 4 spines, of which 
3 form a regular transverse row, the median being longest and furrow spine shortest. The fourth 
spine is situated between the outer two, but adorally and out of line with the series. Near base of 
ray a fifth spine is added to outer end of regular series, and sometimes a smaller spinule stands in line 
with the odd spine, which is about the length of the furrow spine or shorter. 'Furrow spine is 
slightly curved, compressed, and saber-like. The outer spines are faintly curved at the base, are 
tapering, bluntly pointed, and usually directed away from the furrow. External to the outermost 
spine, about midway between it and the innermost inferomarginal spine, is a radiating group of 8 or 9 
ciliary spinelets of different sizes. In the midst of these there is sometimes an inconspicuous 
3-jawed pedicellaria, fairly wide at base, but with tapering, bluntly pointed jaws, scarcely one-third 
the length of adjacent adambulacral spine. These pedicellarise, of which there is never more than 
one to a segment, are not numerous, being present on about half the adambulacrals of some arms and 
almost absent from others. 
Mouth plates are long and narrow. Along the margin are about 8 long, slender, pointed spines, 
which increase in length toward the inner end of the plate, the innermost spine being longest, flattened, 
and directed toward center of actinostome. The adjacent spine is also frequently flattened. Parallel 
with this series, and close to it, on actinal surface, is another series of 4 similar spines. Frequently 
this second series is more or less irregularly grouped in with the first. True marginal spines are 
found on side of plate, one near base of the big inner spine, and 3 or 4 in a cluster, considerably higher 
up, about midway between the first and the roof of the furrow. 
