152 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



apparently the rudiments of a degenerated reticulate skeleton. Rather seldom two or 

 three plates are close enough to be connected by one or two of these secondary plate- 

 lets. Scattered, isolated, tiny, subcircular, spineless platelets are immersed in the 

 membrane, but the numerous smaller deposits of the abactinal membrane of antho- 

 sticta are not present. 



There is a prominent acicular sheathed superomarginal spine, about 4 mm. long, 

 on each alternate superomarginal plate, and two (rarely one) slenderer, tapered, 

 bluntly pointed or flat-tipped inferomarginal spines, invested by a single, common, 

 membrane on each inferomarginal plate. The superomarginal spine is stouter and 

 conspicuously longer than the abactinals, and carries a heavier terminal wreath 

 or subglobular bouquet of pedicellariae. The two inferomarginal spines stand in a 

 longitudinal (sometimes slightly oblique) series on the plate and one is usually a 

 shade slenderer than the other (proximally the adoral, distally the aboral of the two 

 is the slenderer, if any difference is observable). The shrunken sheath bears a thick 

 terminal cluster of pedicellariae. Normally this would extend well beyond the tips of 

 the spines and still does in many cases. 



The marginal skeleton consists of a series of superomarginals somewhat pear- 

 shaped in contour, not directly imbricated as in Pycnopodia, but connected by short 

 arches of two or three overlapping elliptical or ovate-oblong rather stout ossicles, 

 while the inferomarginals usually are connected by two secondary ossicles smaller 

 than the above. Furthermore, alternate superomarginal plates are degenerated and 

 spineless and only a little over half as broad as the spiniferous plates. Both sorts 

 slightly overlap the upper edge of the corresponding narrower but longer, faintly- 

 lobed inferomarginals. There is no difference in the size of alternate inferomarginals. 

 Near the end of the ray the intermediate superomarginal ossicles shrink considerably 

 in size (along with the primary plates) and more nearly represent the condition char- 

 acteristic of the proximal part of the ray of anthostida. But on the outer half of the 

 ray of anthostida the secondary superomarginal ossicles are not present, the primary 

 plates existing as spaced, independent elements except for their connection with the 

 corresponding inferomarginal. As the end of the ray is approached the spineless 

 superomarginal degenerates rapidly and becomes very tiny. In the present species 

 the smaller intermediate plates persist to the tip of ray. The secondary infero- 

 marginal plates, which are usually in couples on the proximal part of the ray, on 

 the distal are reduced to one between a pair of primary plates, and are, relative to 

 these plates, larger than on the proximal part of the ray. In anthostida these plates 

 are only rudimentary on the proximal part of the ray and are entirely lacking 

 distally. 



The terminal plate is rather prominent, armed with numerous short spinelets, 

 the slightly concave adoral abactinal border being flanked by a row of 8 to 10 tiny 

 platelets (absent in anthostida). 



The adambulacral plates, though fairly broad (average 1.25 mm.), are very short, 

 the exposed surface being only about one-third the dimensions of the intervening 

 muscular area. The very slender, tapered, subtruncate, often flat-tipped, spines, 

 one to a plate, form a very even row along the margin of the broad, shallow furrow. 

 The spines are two-thirds to three-fourths as long as the corresponding inferomargi- 

 nals, but scarcely half as thick, and are entirely devoid of pedicellariae. The much- 

 enlarged first pair of postoral adambulacrals are in contact, the sutural margin being 

 decidedly longer than the length of the mouth plates measured on the furrow margin. 



