MUSEUM OF COMPARATIVE ZOOLOGY. 257 



on each side, of which four stand on the mouth-frames, and one on the side 

 mouth-shield : there is in addition a pair which stand at the apex", on the jaw- 

 plate. Five rather thin teeth, shaped like a blunt si;tear-head. Mouth-shields 

 about as broad as long, of a much-rounded diamond-shape, with a sharp angle 

 within; length to breadth, 1.6 : 1.6. Side mouth-shields very narrow within, 

 where they meet, but spreading at their outer end, so as to partly embrace the 

 mouth-shield. Under arm-plates somewhat longer than broad, of an irregular 

 hexagonal form, with a slight notch without; they are small, and occupy not 

 more than a third of the width of the arm. Side arm-plates meeting above 

 and below, clinging close to arm and with a feeble spine-crest. Upper arm- 

 plates about twice as broad as long, of a transverse diamond-shape, with outer 

 angle rounded. Disk sparsely set with short spines, and covered by a skin 

 which hides the thin scales, except here and there. Of radial shields only the 

 outer, rounded ends may be seen, just over the arms.. Genital openings large 

 and extending from mouth-shield nearly to margin of disk. Four slender, 

 smooth, tapering, translucent arm-spines, decreasing in length from above 

 downward, the uppermost one being as long as two joints, while the lowest 

 does not exceed one. No tentacle-scales. Color in alcohol, disk pale gray, 

 arms white. 



Station 260, 291 fathoms, 1 specimen. 



In wanting tentacle-scales this species is especially distinguished. It stands 

 as near to O. abnormis as to any other, but differs in having only four arm- 

 spines and in the arrangement of the mouth-papillse. 



Ophiacantha cervicornis sp. nov. 



Plate V. Figs. 76-78. 



Special Marhs. — Mouth-angles elongated and carrying at their base long 

 spiniform papillae and small peg-like ones at their apex. Arm-spines wide at 

 their base and toothed on the edges. Disk densely beset with short smooth 

 spines. 



Description of an Individual (Station 227). — Diameter of disk 10 mm. 

 Width of arm near disk 2.3 mm. Mouth-angle much elongated and bearing 

 on either side, at its base, four long, pointed spiniform papillae, inside which 

 there are, on either side, five short, pointed tooth-like papilla, and a pair at 

 the apex. Mouth-shields of a transverse oval shape, with a small peak in- 

 ward ; length to breadth, 1 : 1.8. Side mouth-shields of moderate width, 

 meeting within, where they form an acute angle. First under arm-plate much 

 wider than long, with lateral corners rounded and a peak within. The plates 

 beyond have a wide axe-shape, in which the body is narrow with an obtuse 

 angle inward ; the lateral sides are deep re-entering curves, and the cutting 

 edge is represented by the broad, curved outer margin. Side arm-plates meet- 

 ing below and nearly so above, and having a rather feeble spine-crest. The 

 first two upper arm-plates bear a few small tooth-like spines, and are as broad 



VOL. X. — NO. 6. 17 



