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 aljove and 

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

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

 triangular, with an acute angle inward ; the outer margin curved ; the la<> 

 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 sjiines ; the longest one .6"™ long. Beyond the disk the 

 two upper spines attain a length of 1.8°™-. 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. 21-23. 



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

 pillo3 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 Individual. — Diameter of disk, 6"""'. Width of arm without 

 spines, l.G"""-. Mouth-papillte seven or eight on each side and one under the 

 teeth ; the lateral ones are spiniform, the outer 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 very obtuse angle within, a gentle curve without, and re- 

 entering curves on the sides ; length to breadth within the disk, .5 : .7. The 

 first plate, at the corner of the mouth-slit, has each margin curled downward, 



