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



covered with a thick skin, which obscures the radial shields and scaling, except a patch 

 near mouth shield ; the surface is closely set with small spines, about "8 mm. long, whose 

 ends are forked, but which are more or less cased in skin. Seven regular tapering arm 

 spines, smooth, or bearing a few minute thorns ; the upper one somewhat longer ; 

 lengths to that of an arm joint, 4, 3, 2"8, 1"6, 1'6, 1'6 : 1'2. One small blunt, pointed 

 tentacle scale. Colour in alcohol, disk above dull chocolate-brown, lower side and arms 

 pale brown. 



The only essential variation noted was in a larger specimen, with a disk of 18 mm., 

 •which had sometimes as few as seven mouth papillae to an angle. 



Station 298.— November 17, 1875 ; lat. 34° 7' S., long. 73° 56' W. ; 2225 fathoms 

 grey mud. 



Ophiacantha stimulea, Lym. (PI. XIII. figs. 4-6). 



Opliiacantha stimulea, Lym., Hull. Mus. Comp. Zool., vol. v., part 7, p. 141, pL ix. figs. 225-228, 

 1878. 



Disk closely set with small simple spines. Arm spines not thorny. One or two 

 large long tentacle scales. 



(Type specimen from Station 164.) Diameter of disk 7 mm. Length of arm 35 mm. 

 Width of arm without spines 2 mm. Ten or twelve pointed, flat, rather thin mouth 

 papillge, of which the two innermost are largest, the others about equal. Teeth similar 

 to innermost mouth papillae, but larger. Mouth shields wider than long, rather small, 

 bounded without by a curve and within by an obtuse angle. Side mouth shields some- 

 what curved, rather narrow within, where they meet, wide without. Under arm plates 

 wider without, where they are bounded by a gentle curve, than within, where they present 

 an obtuse angle ; lateral sides slightly re-enteringly curved. Upper arm plates f;\n-shaped, 

 with an angle inward. Side arm plates stout and prominent, meeting narrowly above 

 and below, near base of arm. Disk a little puffed, with a constriction in each inter- 

 brachial margin, closely set with small simple spines, which, under the microscope are 

 seen to be slightly rough at their tips ; just over each arm they are much shorter, and 

 extend to the first upper arm plate. Radial shields and scaling wholly obscured by thick 

 skin and spines, except on a small patch next mouth shields. Seven regular, not thorny, 

 nearly cylindrical, rather slender arm spines, which taper slowly to a blunt point ; lengths 

 to that of an arm joint, 2, 3, 2, 1'5, 1'5, 1*5, 1 : "8. Tentacle scales long, pointed, and 

 rather wide ; two on each of first two or three pores, and one on those beyond. Colour 

 in alcohol, white. 



Station 164.— June 12, 1874; lat. 34° 8' S., long. 152, 0' E. ; 950 fathoms; grey 

 ooze. 



This species is distinguished from Ophiacantha segesta by more numerous and 

 different mouth papillae and by stouter arm spines. 



