REPORT ON THE OPHIUROIDEA. 243 



OjMomyces frutectosiis, Lym. (PI. XLIV. figs. 6-9), Bull. Mus. Comp. ZooL, vol. i., 

 part 10, p. 345, 1869 ; 111. Cat. Mus. Comp. ZooL, No. vi., pi. ii. figs. 11-13 ; Bull. Mus. 

 Comp. ZooL, vol. v., part 9, p. 228. 



West Indies ; 77 to 160 fathoms. 



Group III. — Astropliyton-like Ophiurans. 

 Ojihiobyrsa. 



OpMolTjrsa, Lym., Bull. Mus. Comp. Zool., vol. v., part 7, 1878. 



Entire animal clothed in a thick skin, which hides the underlying plates, and is 

 beset on the disk with spines. Arm nearly cylindrical. Side arm plates projecting as 

 short flap-like spine ridges, which bear slightly rough spines on their outer edge. 

 Tentacles large and simple. Few or no mouth papillae, but at apex of mouth angle the 

 teeth and tootli papillfe are represented by a clump of little spines. Two large genital 

 openings in each interbrachial space. 



On examining the under side of the disk skin, it will be seen that the short spines 

 are the outgrowth of small plates which make a minute pavement (PL XLIII. fig. 16). 

 These plates become much larger between the radial shields. The oblong radial shields 

 (T) are small and short, and are attached to small, oval, solid, plastron-like genital plates 

 (o) which cling close to the arm and almost meet on its upper median line. Near the 

 outer end is jointed the short, curved and rather slender genital scale {n), which extends 

 farther inward than the plate. The general external resemblance to OpUomyxa is 

 carried out in the arm plates, whereof the under one is shield-shaped with an angle 

 inward and re-entering curves where the tentacles come out. To it are attached side 

 arm plates shaped somewhat like a shoe sole, and these are continued upward by small 

 round pieces which correspond to upper arm plates. The arm bones, however, are 

 perhaps nearest those of Sigsbeia. They are discoid, with plain, not very thick edges. 

 Their outer face looks like a feeble essay at the arm bone of an Astrophyton. There is 

 the large articulating shoulder (fig. 17, 4), below which is an irregular vertical groove 

 which passes through the place of the absent articulating peg, and is fitted to receive the 

 umbo (fig. 18, 1), which is continued downward by a pillar-like prolongation. The small 

 mouth angle is quite covered above, to the inner edge of the nerve ring, by the thick, 

 swollen, single peristomial plate (v), which is closely soldered to the surrounding parts, 

 and is so large as nearly to connect with its neighbours. The small jaw (c) carries a little 

 bead-like tooth (e). 



See Plate XLIII. figs. 16-18. 



