OPHIACANTHA MARSUPIALIS. 13 



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

 meetmg above, and nearly below, and havhig 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 .S"™' long. Radial 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, especially those of the lowest spine ; lengths to that 

 of an under arm-plate (near the disk) .7, 1.3, 1.2, 1, .8, .6 : .6. Tentacle-scales 

 two, large, pointed oval, lying side by side. The tentacles, especialh' 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. nov. 



. PI I. f. 9, 10. 



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

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



Descnption of an Individual. — Diameter of disk, 3.7""'. Width of arm with- 

 out spines, .9""'. Length of arm, 10"""-. Mouth-papillte 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, 



