1114 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
invested prickle is always sharp. Interradial plates nearly naked, expanded and spatulate at upper 
end. Below they narrow and bend outward in a slight elbow, expanding a bit on the interbrachial 
angle to form 2 distinct condyles for the articulation of proximal marginal plate of each adjacent ray. 
The interradial plate is marked by a shallow longitudinal sulcus or occasionally by two lateral sulcuses, 
and a central low ridge. Abactinal membrane of rays thin and translucent. The basal two-fifths of 
ray', occupied by genital region, is crossed by 32 to 38, usually about 35, transverse, calcareous annular 
ridges or costa? . These ridges begin very nearly at the base of the ray, where they are much closer 
together (1-2 mm.) than over outer two-thirds of genital region (3-7 mm.). Ridges are narrow and 
prominent, composed of imbricating calcareous rods which appear very firmly ankylosed, although 
sutures can usually be distinguished. These ossicles bear numerous microscopic pedicellarise, and a 
longitudinal row of numerous, distinctly spaced, sharp, prominent prickles, which are absent from 
the lateral plates adjacent to each alternate adambulacral. A few of the ridges are incomplete and 
extend only slightly beyond median radial line; but consecutiveridges appear never to join as is com- 
monly the case in the two foregoing species. While often sinuous in the median radial portion, the 
ridges are fairly regular and spring from a lateral plate adjacent to each alternate adambulacral, which 
plate bears the lateral spine, and on the outer two-thirds or three-fourths of the ray, appears firmly 
ankylosed to its neighboring adambulacral plate. The membrane between ridges bears microscopic 
pedicellarise, which are arranged in 1 to 4 narrow bands, according to width of interval. These bands 
are inconspicuous, are parallel with the calcareous ridges, and on some rays are almost entirely absent. 
Beyond genital region the pedicellarise are grouped in transverse lateral bars, and in median radial 
line are scattered. There are a few tegumentary prickles at base of ray, but these do not extend far 
beyond disk. Consequently, especially in a dried specimen, the integument of arms appears fairly 
smooth. 
Ambulacral groove has the appearance of being rather wide and shallow in the genital region. 
Adambulacral plates form a rounded margin to furrow; short (2 mm. long) in genital region; about 
as high as long; conspicuously longer than in B. panopla. On distal portion of ray the plates, as is 
usual, are longer and slenderer, and all are concave in the middle, especially toward furrow. 
Armature as follows: (1) A slender furrow spinelet, invested -with an inconspicuous membranous 
sheath bearing microscopic pedicellarise, situated aborally on furrow margin. At base of genital 
region this spinelet is about 1.5 to 2 mm. long, and seldom exceeds 2 mm. throughout the ray. (2) On 
the actinal surface of each plate a long slender spine articulated to a slight prominence or tubercle. 
On alternate plates this spine is often slightly longer, and placed slightly more laterally, a second 
shorter spinule (3-4 mm.) being present between it and the furrow spinelet. Sometimes this smaller 
actinal spinule is absent, although the longer spine is nevertheless placed more to the outer side of the 
plate. Frequently on plates with 2 actinal spines, the single furrow spinelet is absent. The larger 
actinal spine measures 8 mm. near base of ray, increasing to 13 or 14 mm. at distal limit of the genital 
region, whence it again gradually becomes shorter toward tip of ray. All spines are sheathed in 
membrane, covered with pedicellarise, but the latter do not appear so conspicuous or numerous as in 
the 2 preceding species. Adambulacral plates of distal half of arm bear but one actinal spine. On a 
very few rays there is also but one actinal spine on most of the plates of the proximal half of the ray. 
Some of the actinal spines at base of ray appear to bear a truncate, flaring tip, but these spines are 
longer and slenderer than in either of the foregoing species. Most of them are broken so that it is 
impossible to determine how many possess the enlarged tip. 
The lateral spines are articulated to the lateral plates, adjacent to about every alternate adambu- 
lacral plate or those which have 2 actinal spines. Lateral spines are present beyond tenth adambu- 
lacral plate, and thence very rapidly increase in length, so that in mid-genital region they attain 12 or 
13 mm., which is increased occasionally to 15 mm. at the distal limit of the costal region. Membrane 
and pedicellarise present. 
Actinostome very large, 20-21 mm. in diameter. Mouth plates fairly large, deeply excavated on 
side toward furrow for accommodation of first tube foot. Actinal surface of plate plane. Armature 
as follows: (1) A short spinelet (1.5 mm. long) situated on the middle of the margin toward actino- 
stome, and a second slightly larger spinelet, on the tip of the lateral prolongation, directed across the 
mouth of ambulacral furrow. (2) On extreme outer end of plate is a stout tapering actinal spine about 
4 or 5 mm. long. One of the spines of two companion plates is sometimes shorter than the other. 
Except for this single spine the general surface of the mouth plate is smooth. All the spines bear 
