REPORT ON THE OPHIUROIDEA. 181 



Ophiacantha tuberculosa, Lym. (PI. X. figs. 1-3). 



Ophiacantha tuberculosa, Lym., Bull. Mus. Comp. Zool., vol. v., part 7, p. 137, pi. viii. figs. 

 204, 205, 1878. 



Disk wrinkled and beset with coarse grains ; four smooth stout arm spines. 



(Type specimen from Station 210.) Diameter of disk 6 - 5 mm. Length of arm 

 32 mm. Width of arm without spines 2 mm. Seven stout blunt mouth papillae, 

 whereof the innermost is spearhead-shaped and stands under the teeth, which are four in 

 number, flat and square, with rounded corners. Mouth shields small, much wider than 

 long, with an obtuse angle within and a little peak without ; length to breadth, '8:1. 

 Side mouth shields short, nearly crescent shape, with the curve outward ; scarcely 

 meeting within. Under arm plates thick and distinct, four-sided, somewhat broader 

 than long, with outer side curved and the others nearly straight, except second plate, 

 which is nearly pentagonal, with a very obtuse angle within. Side arm plates slightly 

 projecting, meeting narrowly below and not at all above. Upper arm plates thick and 

 well marked, four sided, with outer corners rounded, much wider without than within. 

 Disk contracted in interbrachial spaces, with deep radiating furrows between the narrow 

 radial shields, which are completely hidden, as well as the disk scales, by the skin and by 

 numerous small conical tubercles, which are larger and closer set on the radial shields. 

 Four stout, blunt, cylindrical, smooth arm spines ; upper one much largest; lengths to 

 that of an arm joint, 2, 1*4, 1, 1 : 1. One rather small tentacle scale, longer than wide, 

 pointed, and not encroaching (as is usual in the genus) on the under arm plate. Colour 

 in alcohol, very pale brown. 



This species is one of the most aberrant in the genus ; the arm spines, smooth, and 

 only four in number, and the minute disk tubercles, instead of thorny grains, remind one 

 rather of Ophiocoma. Indeed, Ophiacantha bidentata and Ophiacantha vivipara, which 

 somewhat resemble this species, have been described under Ophiocoma ; but the general 

 structure is that of a true Ophiacantha. 



Station 210.— January 25, 1875; lat. 9° 26' N., long. 123° 45' E. ; 375 fathoms; 

 mud. 



Ophiacantha placentigera, Lym. (PI. XXVIII. figs. 15-17). 



Ophiacantha placentiger a, Lym., Anniv. Mem. Bost. Soc. Nat. Hist., pi. ii. figs. 20-22, 1880. 



One very large, flat tentacle scale. Six cylindrical, tapering, nearly smooth arm 

 spines. At inner point of each under arm plate is a diamond-shaped raised figure. 



Diameter of disk 9 "5 mm. Width of arm, close to disk without spines, 2 mm. Five 

 spaced mouth papillae on each side of mouth angle, the two outermost, large, squarish 

 and flat, the three inner ones more pointed ; and the one at the apex short and blunt. 

 Mouth shields broad triangular, with rounded corners, and a blunt angle inward. Side 



(zool. chall. exp. — part xiv. — 1882.) O 24 



