OPHIACANTHA MARSUPIALIS. 13 



so as to make a sort of sheath to the mouth-tentacles. Side arm-plates large, 

 meeting above, arid nearly below, and having a narrow, prominent ridge for 

 arm-spines. Upper arm-plates small, irregular diamond-shape, with a rounded 

 angle without and within, and an acute angle on each side ; on the median 

 line a hump or ridge ; length to breadth, .6 : .7. Disk finely scaled below, 

 about six scales in the length of a mm., and with a short thin spine here and 

 there ; above, the scaling is not apparent, and the surface is pretty closely 

 beset with short slender spines about .5 mm long. Kadial shields covered, their 

 outer ends only being marked by swellings. Arm-spines usually six, near 

 disk, the second and third longest ; flattened, somewhat glassy, with the 

 edges strongly serrated, especialty those of the lowest spine ; lengths to that 

 of an under arm-plate (near the disk).?, 1.3, 1.2, 1, .8, .(3 : .6. Tentacle-scales 

 two, large, pointed oval, lying side by side. The tentacles, especially those 

 of the mouth, are thick and smooth. 



Color pale greenish, in alcohol. 



Dr. William Stimpson ; off Sombrero Key, Florida, 240 fathoms. Hassler 

 Expedition; Barbadoes, 100 fathoms. 



Ophiacantha marsupialis sp. now 



PL I. f. 9, 10. 



Special Marks. — Upper arm-plates diamond shape ; side arm-plates meeting 

 above ; small oval radial shields ; a few stout, short thorns on the disk. 



Description of an Individual. — Diameter of disk, 3.7 mm . Width of arm with- 

 out spines, .9 mm \ Length of arm, 10 mm . Mouth-papilla? eleven to each mouth- 

 angle ; thin, spiniform ; of these two on either side are much longer than the 

 rest and stand on the broad and conspicuous jaws, just inside the mouth- 

 shields ; the rest are much smaller, and make a clump at the inner point of 

 the angle, some standing on the jaws and some on the jaw-plate. Mouth- 

 shields wide diamond-shape ; length to breadth, .4 : .5. Side mouth-shields 

 narrow, of about uniform width ; not extending beyond the mouth-shields ; 

 meeting within. Under arm-plates narrow, longer than broad, curved with- 

 out, re-enteringly curved on the sides, and presenting a rounded angle 

 within ; length to breadth within the disk, .4 : .2. The first plate, instead of 

 being rudimentary, differs little in size and shape from the rest. Side arm- 

 plates meeting fully above and nearly below. Upper arm-plates diamond-shape, 

 with one of the angles rounded and directed outward ; length to breadth. 



