1116 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
costal region, one opposite each adambulacral plate, throughout ray. Variation d: One specimen from 
station 4131 has more numerous annular ridges, 35 to 40. The difference is solely due to the greater 
number and prominence of the secondary ridges, which practically occur in each intercostal space, and 
reach nearly or quite to the adambulacral plates. They differ from the primary ridges in that there 
is no larger (infero-) marginal plate joining the slender ossicles with the corresponding adambulacral 
plate. The secondary ridges are therefore never fused with the adambulacral plates, a small free 
space always intervening. Variations a and b: Secondary costee very few and rudimentary. Bands 
of pedicellarise in intercostal spaces are prominent and saccular, and the ridges are also invested in a 
soft membrane covered with minute pedicellarite. Primary costae, 18 to 26. 
Ambulacral furrow wide and shallow. Adambulacral plates (1.5 to 2 mm. in length) are about 
twice as long as wide (in the middle) and rather more than twice as long as high (seen from side). 
Plates constricted in middle, but especially concave on the furrow face. Armature, especially the 
furrow spinelets, somewhat variable in arrangement and number. The typical form will be first 
described, and then the several variations. Armature in type and similar specimens is simplest of all. 
There is but one furrow spinelet situated near the adoral end of the plate, except on the 6 to 12 
proximal plates, where an exactly similar spinelet is, present on the extreme aboral end. Both 
spinelets, which are directed across the furrow, are about 1 to 1.25 mm. in length, are invested in a very 
thin membranous sheath expanded at the tip, and there covered with microscopic pedicellarise. On 
the actinal surface, rather nearer to the aboral edge than to the center of the plate, is a delicate and 
fragile spinule about 4 mm. in length, invested in a delicate membrane on which are microscopic 
pedicellarise. This spinule is more delicate than is usual in this genus for the principal adambulacral 
spine. On account of their extreme fragility, nearly all of these spines are broken in the type series. 
Variation a: On the proximal 12 or 15 plates (basal fifth of ray) there are 2 adoral furrow spinelets, 
1 right above and slightly aborally from the other, and 1 aboral spinelet as in the type. Barely 
there are 3 adoral spinelets at the very base of the ray. On the next few plates, about the fifteenth to 
twentieth, the aboral spinelet is missing. On the outer three-fourths of the ray the furrow armature 
is that of the type — 1 adoral spinelet. The actinal spine is a trifle stouter and longer than the other 
specimens (7 mm. in mid-genital region). (1 specimen, station 3817.) Variation b: Besembling a; 
proximal plates with 3 furrow spinelets, 2 adoral and 1 aboral. The succeeding 2 or 3 plates lack 
the aboral spinelet. Outer half of ray as in type. Actinal spine as in type, not so stout or prominent 
as in a. On some rays the aboral spinelet extends nearly to middle of ray, and the 2 or 3 succeeding 
plates may have only 1 adoral and 1 aboral spinelet. (2 specimens, stations 3892, 4041.) Variation c: 
This is near the typical form, the only difference being that the plates with 1 adoral and 1 aboral 
spinelet extend about one-third the length of the ray instead of being confined to its immediate base. 
(2 specimens, stations 3914, 4096.) Variation d: Multicostate form with rather stouter actinal spines 
than type. Furrow armature is practically the same as type, except that occasionally on basal third 
of ray there will be 2 instead of 1 adoral spinelet. (1 specimen, station 4131. ) If the furrow armature 
is represented graphically by a common fraction, the numerator standing for the aboral spinelet, and 
the denominator for the adoral spinelet of each plate, the typical formula would be -J. If the ray be 
represented by a line, the base at the left, then the proportion of plates with each type of armature 
to the whole ray in the different varieties will be about as follows: 
Type: 
10 0 
1 1 
1 1 
0 
0 
‘ 1 
0 
3"° r ’2 
2 " 
1 
1 
1 
lor l . 
0 
0 
o 
2 1 
1 
1 
i 
0 
0 
1 1 1 
/ i 0 
(rarely-) 
D: 
1 
_0 
1 
0 
1 
