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



sharp, close- set papillae. Scaling of disk beset with granulation. Arms long and rather 

 stiff, arm spines few (three) and smooth, arranged on the ridges of the side arm plates. 

 One very large tentacle scale on the side arm plate, and others, minute, on the under 

 arm plate. Two long genital openings in each interbrachial space. 



The genus stands near Oj)liiocnida, but is distinguished by the numerous mouth 

 papillaj arranged as in Ophiura, and by the singular tentacle scales. 



By its internal, even more than by its external structure, Opliioplax is separated 

 from such genera as Op)kiocnida. While the slender genital plates, thin genital scales, 

 and arm bones with a forward projection remind us of the Amphiurse ; the radial shields, 

 continued inward by a line of large overlapping scales, suggest Ophiocoma ; and the wide 

 spreading, solid mouth angles, with large tentacle sockets, and the thick peristomial 

 plate, in two pieces, are even larger than in Ampjliilepis. 



See Plate XLI. fig. 7. 



Species of Opkiop)lctx not herein described. 

 Ojihioplax Ijungmani, Lym. (PL XLI. fig. 7). 



Ophioplax Ijungmani, Lym., 111. Cat. Mus. Comp. Zool., Xo. viii., part 2, p. 22, 1875, pi. ii. rigs. 

 24, 25 ; Bull. Mus. Comp. Zool., vol. v., part 9, p. 228. 



West Indies ; 80 to 127 fathoms. 



Ophiostigma. 

 OpMostigma, Ltk., ViJ. Meddel., Jan. 1856. 



Disk granulated. Teeth. No tooth papillae. Basal mouth papillae very long, stout, 

 and broad ; the others small and few, arranged so as to cover the end as well as the sides 

 of the angle of the mouth. Arm spines three, short, smooth, arranged along the sides of 

 the side arm plates. Side mouth shields large ; nearly, or quite, touching, so as to form 

 a ring round the mouth. Mouth apparatus, as a whole, forming a distinct, raised 

 pentagon. Two genital openings, beginning outside the mouth shields. 



This shares with Ophiothammis a curious skeleton modification. It is, that the geni- 

 tal plates instead of occupying their normal position at the sides of the arm, lie above it 

 and hide it (PI. XLII. fig. 16, o). So that the thin warped genital scales {n) are below, 

 and their plane is at right angles with that of the plates. The disk scaling is very 

 coarse, thick and irregular, with large three-sided radial shields having prolonged angles. 

 The mouth frames are compact and plain, without deep grooves. They have a rather 

 small, rounded peristomial plate of a crusty consistency. The jaw is small and soldered 

 with the jaw plate, as in Amphiura, 



See Plate XLII. fig. 16. 



