82 THE VOYAGE OF H.M.S. CHALLENGER. 



truncated angle, with corners rounded ; the rest of the under arm plates are very small, 

 nearly or quite semicircular, with a little peak inward. Side arm plates slightly flaring 

 outward, meeting broadly below, where they form most of the under surface of the 

 arm ; separated above by upper arm plates, which are four sided, with outer edge wider 

 than inner, and curved ; lateral sides slightly re-enteringly curved. Disk flat and thin, 

 covered with small, transparent, delicate scales ; six small, rounded, widely separated 

 primaries, one in the centre and one to each brachial space ; outside these there are two 

 similar plates in each interbrachial space, one towards the centre and one near the 

 margin ; along the margin there are two irregular rows of small plates, somewhat broader 

 than long. Eadial shields triangular, with a rounded angle inward, widely separated by 

 the disk scaling ; length to breadth r5 : 8. Lower interbrachial space covered by 

 delicate, nearly transparent sealing, which also hides the genital scales, except their outer 

 tips, just outside the radial shields, which bear an arm comb of three or four minute 

 papillee. Genital opening quite long, extending from the outer end of side mouth 

 shields to edge of disk. There are large tentacle pores, but no scales on any of the 

 pores. Near base of arm there are three small, delicately tapering arm spines, situated 

 on the outer edge of the side arm plate ; the upper is about two-thii-ds the length of an 

 arm joint, and the lowest about half as long ; farther out there are but two spines. 

 Colour in alcohol, white. 



On the above specimen no tentacle scales could be seen, but on others some pores, at 

 any rate, are furnished with a single minute one. 



Station 325.— March 2, 1876 ; lat. 36° 44' S., hmg. 46° 16' E. ; 2650 fathoms; grey 

 mud. 



Ophiocten hastatum, Lym. (PI. IX. figs. 10, 11). 



OpJiioeten hastatum, Lym., Bull. Mus. Comp. Zool., vol. v., part 7, p. 103, pi. v. figs, 133, 134, 

 1878. 



Disk with minute thin scales, among which appear weU-marked primary plates. 

 Three tapering arm spines, the upper much the longest and largest. One minute tentacle 

 scale. 



(Type specimen from Station 146.) Diameter of disk 9 mm. Width of arm close to 

 disk 2 mm. Four or five short, squarish, close-set mouth papillae on each side, with one 

 much larger at apex 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, which is slightly 

 rounded ; the remainder of the under arm plates are much wider than long, and nearly 

 semicircular, with a slight peak inward, and outer side strongly curved. Side arm plates 



