CLARK: OPHIUROIDEA. 451 



Ophiomusium tripassalotum,' sp. nov. 

 Plate 5, fig. 3, 4. 



Disk, little arched, 0.5 mm. across; arms very slender about 33 mm. 

 long. Disk covered by about 50 rather small plates, slightly swollen 

 around the margins, among which the primary plates can be distin- 

 guished; a large marginal plate in each interradius, with a smaller 

 plate directly above it are much the largest of the disk-plates. Radial 

 shields large, distinctly longer than wide (but scarcely equal to one 

 half radius), l)roadly in contact, but at distal end separated very 

 slightly by a small triangular plate. On each side of this plate is a 

 smaller, transversely elongated, conspicuously swollen plate, the three 

 forming a noticeable group at the base of each arm. Upper arm- 

 plates minute, triangular, very widely separated, but remarkably 

 persistent, present nearly or quite to the tip of the arm. Entire 

 upper surface of disk and arms quite smooth, not at all shagreened. 

 Interbrachial areas below covered by 6-12 smooth, irregular plates 

 of very diverse sizes and arrangement. Oral shields pentagonal, 

 longer than wide. Adoral plates long, straight, and narrow, the 

 length fully 3-4 times the width. Oral plates evident, but much 

 smaller than adorals. Oral papillae 5-7 on each side, very low and 

 wide and not very distinct; the distal ones are widest. First under 

 arm-plate minute about twice as long as wide; second under arm- 

 plate much larger, shield-shaped but greatly elongated; it is widest 

 distally, but even there is not half as wide as its length; third under 

 arm-plate small not much longer than wide; no under arm-plates 

 beyond third arm-segment. Side arm-plates relatively large and long, 

 considerabl\- swollen proximally, meeting fully above and below, but 

 with no trace of a longitudinal groove on either surface of arm; each 

 plate carries, on its lower distal corner, 3 small, blunt, subequal, peg- 

 like arm-spines, about one fourth as long as arm-segment. Tentacle- 

 pores present on arms only beside the proximal part of the under 

 arm-plates on the second and third segments; each is provifled with 

 a large tentacle-scale. Color (dried) : — very light, nearly white. 



Station 3690. Paumotu Islands: 2 miles west of Hao Atoll. 

 812 fms. Bott. temp. 37.6°. Co. s. 



One specimen. 



The persistence of the upper arm-plates, while the under ones are 



' Tpe?s = three + TraffffaXos = ii pep, in reference lo the three peg-like arm-spines. 



