320 BULLETIN OF THE 



form. Below, the disk is covered by half a dozen plates, in each interbra- 

 chial space, arranged in two concentric rows ; besides which a wide genital 

 plate runs along the slit, bearing on its edge a row of short, stout, rounded 

 papillae, which run from the second under arm-plate upwards along the 

 outer edge of the radial shield to a point about opposite the lateral corner 

 of the upper arm-plate. Arm-spines three, very short and small ; lengths 

 to that of under arm-plate (3d joint) .2, .2, .2 : .4. At, and beyond the 

 first joint outside the disk, the middle spine takes on the form of a broad, 

 strong hook, having two curved teeth on the upper edge. At the tip of 

 the arm there are but two spines, of Avkich the upper is the hook. Tenta- 

 cle scales of the mouth-tentacles six ; three on each side of a very narrow 

 incision, which is squeezed between the side mouth-shield (which bears 

 three of the scales) on one side, and the large first under arm-plate and the 

 outermost mouth-papilla on the other side. Second pore with six scales, 

 arranged round a narrow oval ; third pore, two scales, side by side ; and 

 those beyond, only one scale, which, at some distance out on the arm, is 

 very minute and difficult to be seen. 



Color, in alcohol, white. 



Variations. — Another smaller specimen had the disk 3 mm. and the arm 

 9 mm. The mouth-shields were proportionately longer than in the first 

 mentioned, — a variation common to the whole genus. 



Two specimens, in 377 fathoms, south of Rebecca Channel. 



The plates on the disk indicate that these specimens, although by no 

 means fully grown, are yet large enough to show the adult characters. 

 Thus O. Sarsii, with a disk of 4.5 mm. (see LUtken Addit. ad Hist. Oph. Pt. 

 T, PI. I, fi"-. 3), is more young, in this respect, than O.falcifera, and yet has 

 taken on all the parts needed for ready recognition of the species. We 

 may look for an adult of this curious species about the size of 0. Sarsii, or 

 rather smaller, and having a large number of small plates on the disk. The 

 stout, double-toothed hook, as a middle arm-spine, is only an embryonic 

 organ carried forward. In the very tip of the arm of 0. accrcata I have 

 found, on the last fourteen joints, only two spines; and of these the upper 

 one was flattened, and bore on its upper edge (just as in 0. /ale if era) 

 about nine microscopic, hooked teeth. It may be that the fully grown 

 O.falcifera has the middle hook, at the base of the arm, so overgrown as 

 to form a stumpy spine. 



Ophiocten depressum Lyman, sp. nov. * 



Special marks. — Disk very thin and flat, with a sharp edge. The 

 granules of the disk are numerous, but irregularly scattered ; none on the 



* This species departs a good deal from the typical Ophiocten. The disk granulution 

 is not continuous, but scattered; there are no combs of spines on the outer edges of the 



