54 OPHIOCTEN KROYERL 



great encroachment of the side arm-plates ; bounded without by a 

 gentle curve, and within by two Imes a little re-enteringly curved, and 

 converging on the middle line in a slight peak ; length to breadth 

 (sixth plate), .3:1; sometimes the inner side is bounded b}^ an almost 

 straight line ; first plate longer than those beyond, broad triangular, 

 with angles rounded, and one of them directed inward ; length to 

 breadth, .7 : .8 ; second plate of nearly the same shape, but shorter and 

 more rounded. Side arm-plates encroaching below to an unusual 

 degree, so that, at the sixth joint, the length of the line of juncture of 

 the side arm-plates, is to the length of the under arm-plate as .4 : .3 ; 

 near the end of the arm, almost the whole under surface is occupied by 

 the side arm-plates, the under arm-plates being reduced to little semi- 

 circular scales. UjDper arm-plates regular, broader than long, narrower 

 within than without, bounded on outer, inner, and lateral sides by 

 straight lines ; length to breadth (fourth plate), .7 : 1.4. Disk plates 

 and grains : above, remarkably flat, and closely soldered together, so 

 that their outlines are hard to see ; below, the scales are larger, more 

 swollen, and easily distinguishable ; in the centre, above, there is a 

 rosette of six large, round, separated primary plates, the largest having 

 a diameter of about 1°"° ; there are also a few other smaller primary 

 plates in the brachial and interbrachial spaces ; of the disk granules 

 there are about GO to a square mm. Radial shields longer than broad, 

 widely separated, irregular, swelled and rounded without ; length to 

 breadth, 1.2 : .8. There is a continuous line of short, pomted papilla?, 

 running along the genital slit, and passing along the edge of the disk, 

 over the top of the arm ; of these, those along the genital slits are the 

 most slender ; the stoutest papilla? are those standmg just over the arm, 

 on the sides, about five in number, and having a length of .2°"° ; the 

 four or five lying over the arm, on the middle line, are smaller, and 

 stand a little lower ; the first, second, third, and sometimes fourth, 

 upper arm-plates have papillse along their outer side ; of these the first 

 plate has the longest. Arm-spines three, rounded, tapering, very sharp ; 

 two upper ones much the longest ; lengths to that of under arm-plate 

 (sixth joint), 1.1, .9, .5 : .3. Tentacle-scale triangular, as broad as long, 

 with an angle outward ; on the first three or four joints an additional 

 scale on the outside of the pore. Color, in alcohol, light gray. 



Variations. — A specimen with a disk ILo""" in diameter had arms 

 about 36°"°' long ; the color, in alcohol, was brownish white ; there Avere 

 ten or eleven mouth-papillge, the outer broad one being broken in two 

 or three. The species grows as large as 15'°™- for the diameter of the 

 disk. It has been taken at Spitzbergen (Professor Kroyer), and on the 

 coast of Greenland, in fifteen to twenty fathoms water, muddy bottom 

 (Barrett). 



