ARCTIC SEA TO THE WEST OF GREENLAND. 65 



Genus OPHIOCTEN, Lutken. 



OpUocten, Lutken, Vid. Meddel. 1854. 



Disk very flat, with margin forming a sharp angle; covered with imbricating 

 scales and a superficial squamo-granular layer, through which only portions of the 

 radial shields and primary plates are visible. No disk-incisions, the disk forming a 

 little arch over the base of the arms. A row of papillae edges the genital slit, and 

 passes over the arm along the disk-margin, continuous with the series from the other 

 side. The mouth-shields are scutiform, and are prolonged into the interbrachial space. 

 The first group of tentacle-scales pass inwards, close to the angle of the jaws. Three 

 arm-spines, arranged along the outer edge of the side arm-plate, the two upper spines 

 being much the largest. 



OPHIOCTEN SEBICEUM, Forbes, sp. Plate IV, Figs. 8-10, 14.. 



Ophiocten Kraeyeri, Lutken, Vid. Meddel. 1854, p. 8. 



Ophiura sericea, Forbes, Sutherland's Journ. Voyage Baffin's Bay, Appendix. 



A typical specimen should have the outline of the disk, seen from above, perfectly 

 circular, without arm-notches and without straight lines to the margin of the interradial 

 areas. The disk is slightly tumid above ; and the sharp margin merges into a more 

 largely scaled and flatter under-disk. Disk tessellated with circular plates, one in the 

 centre, five around at some distance, and a few others, but all separate and ornamented 

 with radiating lines of cells, all being surrounded and overlapped by a derm of minute 

 circular scales cellular in aspect. The radial shields, which are wide apart, are larger 

 than the other plates, narrowest aborally and broadest within ; obliquely placed, their 

 distal end being arched and free ; and between them, under the derm, are some rudi- 

 mentary upper arm-plates. There are distinct radial scales projecting beyond the radial 

 shields ; and on their distal edge from 5 to 7 spinules with narrow bases, swollen cylindro- 

 conical trunks, and rather angular and sharp terminations are visible. These are in 

 a row ; and there are others in some instances projecting from the cells of the derm 

 between the radial shields, and, deeper still, from the rudimentary upper arm-plates. 



The upper arm-plates, broad, short, and convex near the disk, form much of the 

 arm ; and usually the first five or six large ones are covered with a row of smaller 

 spinules than those on the edge of the disk, which project along the line of, and close 

 to, the arm, extending, in some, along the whole distal curve. After the fourth they 

 diminish in number ; and one or two only are seen on the six arm-plates further out. 



The upper arm-plates increase gradually in length, and only diminish in breadth 

 far out, and at last become more or less triangular in outline, whilst quite at the top they 

 are long, narrow, triangular, and separated by the side arm-plate. In some specimens 

 there are no spinules on the upper arm-plates. 



Beneath, the scaling is larger and overlapping in the interbrachial spaces, and is 







