MUSEUM OF COMPARATIVE ZOOLOGY. 103 



A young 0. sericcum (disk 7.5 mm.) was very like a still smaller 0. gracilis (disk 

 6.8 mm.), which had the arm-comb less marked ; but other specimens had it 

 just the same. A number of specimens marked as 0. sericeuvi (young) and 

 0. gracilis showed variations in number of papilla) along the genital openings, 

 coarseness of disk-scales, more or less pointed tentacle-scales, and length of 

 spines ; but all these variations seem common to both, in a greater or less de- 

 gree. The two specimens of the "Challenger" E.\pedition showed no valid 

 difference with the half-grown 0. sericcum, except in absence of papillae along 

 the genital opening ; but two specimens from George's Bank, off Massachusetts, 

 were in this respect intermediate, and had hardly any jjapillaj in that region. 

 Off Marion Island, 50 - 75 fathoms, 2 specimens. 



Ophiocten hastatum sp. nov. 



Plate V. Figs. 133, 134. 



Special Marks. — Disk with minute thin scales, among which appear well- 

 marked primary plates. Three tapering arm-spines, the upper much the 

 longest and largest. One minute tentacle-scale. 



Description of an Individual (Station 146.) — Diameter of disk 9 mm. 

 "Width of arm close to disk 2 mm. Four or five short, squarish, close-set 

 mouth-papilla3 on each side, with one much larger at ape.x of jaw, having two 

 small bead-like ones at its base. Mouth-shield rounded pentagonal, having 

 a broad angle within. Side mouth-shields long and narrow, of about equal 

 width, nearly or quite meeting within. First under arm-plate larger than any 

 of the others, four-sided, with inner side much narrower than the outer, whicli 

 is slightly rounded ; the remainder of the under arm-plates are nmch wider 

 than long, and nearly semicircular, with a slight peak inward, and outer side 

 deeply curved. Side arm-plates somewhat swollen and flaring outward, meet- 

 ing broadly below ; separated above by the upper arm-plates, which are some- 

 what arched, with the inner side narrower than the outer, which is curved. 

 Disk round, smooth, and flat, covered, above and below, with minute thin scales ; 

 in the centre are several rounded primary plates, and one of nearly equal size 

 in each interbrachial space. Radial shields pear-seed shape, witli inner angle 

 blunt, and outer corners rounded ; separated their entire length by fine over- 

 lapping scales. Genital scales hidden, except their tips, outside the radial 

 shields, which bear an arm-comb of a few minute papillec, as does sometimes 

 the first upper arm-plate. Three slender, cylindrical, tapering, pointed arm- 

 spines, the upper one being much longer and larger tlian the two lower ; lengths 

 to that of an arm-joint 3.4, 1, .8 : 1. Tentacle-scales minute and rounded ; 

 there are two or three to each of the second mouth-tentacles ; usually one on 

 the outside of the basal pores, and one on the inside of the pores farther out 

 on the arm. Color in alcohol, disk nearly white ; arms above pale gray. 



Station 78, 1000 fathoms, 2 specimens. Station 146, 1375 fathoms, 12 -j- 

 specimens. Station 163, 1100 fathoms, 12 -f- specimens. 



