232 THE VOYAGE OF H.M.S CHALLENGER. 



Species of Opkioblenna not herein described. 



Ophioblenna antillensis, Ltk., Addit. ad Hist., part 2, p. 137, pi. iv. fig. 4, 1859. 



West Indies. 



Ophioscolex. 

 Ophioscolex, Miill. & Tr., Syst. Ast., 1842. 



Disk covered by a thick naked skin, which conceals the very fine underlying scaling, 

 and which is continued over the arms. There are teeth and mouth papillae, and in some 

 species {Ophioscolex glacialis) a few tooth papillae. Arm spines smooth and covered with 

 thin skin. No upper arm plates. Two genital openings in each interbrachial space. 



Seen from the inside, the apparently naked disk skin is found to cover a delicate coat 

 of very fine scales. Just by the arm, at the margin of the disk is a very small flat slightly 

 curved radial shield (PI. XLII. fig. 2, I), and connected with it, a miniature genital scale 

 (n), flat and curved, and a genital plate (o), with a rounded tapering shaft, and a clubbed 

 head. This apparatus is smaller than in any other genus. The arm bones are peculiar ; 

 they are long and flat on top with a shallow median canal (fig. 2,,w), while their lower 

 surface is, on the contrary, strongly grooved for the central canal, and the tentacle sockets 

 and muscle fields are deep hollows. Their outer and inner faces are low and wide, with 

 a minute articulating peg, above which rises a large shoulder to receive the umbo of the 

 next bone. Not less peculiar are the mouth frames (fig. 3,f), which, instead of being- 

 more or less flaring, as is usual, are compact, destitute of wings, and almost cylindrical. 

 They are prolonged inward by three peristomial plates, two inclined to each other and the 

 third filling the open angle (fig. 3 v,v), which are of such size as completely to cover the 

 mouth angle, except the minute jaw plate which carries sharp, spine-like teeth (d"). In 

 its lower aspect the mouth angle is large, with a small mouth shield (fig. 4, a) and large 

 long side mouth shields. 



See Plate XLII. figs. 2-4. 



'O' 



Table of Species of Ophioscolex. 1 



About seven small peg-like mouth papillae to each angle. No tentacle scale, . Ophioscolex glacialis. 



About eleven small peg-like mouth papillae to each angle. One small tentacle scale, Ophioscolex purpureas. 



Nine sharp, conical mouth papilla? to each angle. A long flap of skin in place of a ) 



... f Ophioscolex stimpsonii. 



tentacle scale, . . . . . . . . • ) * * 



Fifteen mouth papillae to each angle, whereof the three outer ones are long, flat, 1 , 



. .. r. , , , \ Ophioscolex dentatus. 



spiniform. One tentacle scale, . . . . . ) ± 



Seventeen to nineteen small, close-set, tooth-like mouth papilla? to each angle. One ) 



, , ,. ( Ophioscolex tropicus. 



tentacle scale, sometimes none, ...... > - 1 * 



1 Ophioscolex coppingeri, Bell., Proc. Zool. Soc, June 4, 1881, p. 98; West Coast of Patagonia. This species is 

 described as having dorsal plates on the arms, but Professor Bell has since written me that these are really the upper 

 sides of the arm bones. 



