12 OPHIACANTHA HIRSUTA. 



and those beyond it, squarish, with a slight peak within and the sides re-en- 

 teringly curved. Side arm-plates very large, widely meeting above and 

 below ; their outer portion rises in a thick ridge, to carry the arm-spines, 

 which gives a knotted look to the arm (Fig. 18). Upper arm-plates small, 

 triangular, with an acute angle inward; the outer margin curved; the lat- 

 erals re-enteringly curved ; length to breadth, .5 : .5. The outer part of each 

 plate is bent downward. Disk strongly contracted in the interbrachial 

 spaces, giving to it a star shape. Above, closely set with minute stumps, 

 each bearing a crown of four or five thorns and sitting on a thin round disk- 

 scale which is not readily seen. There are about six stumps in the length 

 of a mm. Below, the interbrachial space is naked, or has but few stumps. 

 Radial shields only visible at their outer ends, as two narrow swellings lying 

 in contact. Arm-spines seven, the upper very long ; all of them slender, 

 glassy, and with a few sharp thorns. The joints within the disk have four 

 short, very jagged spines; the longest one .6 mm long. Beyond the disk the 

 two upper spines attain a length of l.S mm -. Tentacle-scales long and narrow ; 

 one to each of the tentacles, which are small and slender. 



Color, in alcohol, yellowish-brown. 



Hassler Expedition ; Barbadoes, 100 fathoms. 



Ophiacantha hirsuta sp. nov. 



PI II. f. U - 23. 



Special Mar fa. — Jaws elongated, and bearing about seven spine-like pa- 

 pillsB on each side, besides one larger under the teeth. Disk beset above with 



short fine spines. Arm-spines serrated. Two large tentacle-scales. Radial 

 shields covered except their outer ends. 



Description of an Imliviiliutl. — Diameter of disk, 0""". Width of arm without 



spines, 1.6 Mouth-papillse Beven or eighl on each side and one under the 



teeth ; the lateral ones are spiniform, tl uter ones longest, and all mounted 



on the jaws, which are prolonged in an acute angle; the papilla under the 

 teeth is broader and diamond-shaped. Mouth-shields wider than long, rounded 

 diamond-shape; length to breadth, .6 : .9. Side mouth-shields narrow. 

 slightly widened without) meeting within. Under arm-plates wider than 

 long, bounded by a verj obtuse angle within, a gentle curve without, and re» 

 entei ing cut ves on the Bides ; length to breadth \\ ithin the disk. ,6 : .7. The 

 firsi plate, at the corner of the month-slit, has each margin curled downward. 



