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



Ophiolebes humilis, Lym. 



Ophiadis humilis, Lyru., Bull. Mus. Comp. Zool., vol. i., part 10, p. 329, 1869. 

 Florida; 125 to 324 fathoms. 



Ophiomitra. 

 Ophiomitra, Lym., Bull Mus. Comp. Zool., vol. i., part 10, 1869. 



Teeth. Numerous (7-11) small, nearly equal mouth papilla?. No tooth papilhe. 

 Disk flat, circular, and erect, covered with scales and wide radial shields, and beset with 

 thorny spines or stumps. Arm spines rough. Side arm plates large and nearly or 

 quite meeting above and below, two genital openings in each interbrachial space. 



So far as concerns the arms and the chewing apparatus, this is an Ophiacantha ; 

 but the disk, with its large naked scales and broad radial shields, separates it from that 

 genus, which is characterised by the long, very narrow, radial shields, covered, together 

 with the disk, by a thin skin bearing more or less thorny appendages. 



In typical species (Ophiomitra valida) the arm spines are solid, like those of 

 Ophiocamax ; but others (Ophiomitra chelys) have them hollow, like Ophiacantha. 

 The radial shields are always large and wide, sometimes flat (Ophiomitra valida) at 

 others countersunk in a sort of fold (Ophiomitra chelys). The strong mouth angles have 

 a thick, single, swollen peristomial plate (removed in PL XLI. fig. 4), which covers a 

 very deep nerve ring (it). The genital plate is short and club-like, with a short, 

 curved, blade-like scale. This scale in Ophiomitra chelys is short, straight, and rounded. 

 The first free arm bone has a lozenge-shaped top, with a sunken centre (w'). On their 

 outer face, the arm bones, which are much wider than long, have very prominent ten- 

 tacle sockets (fig. 5r), while the inner face has flat wings and a prominent umbo (fig. 6). 



See Plate XLI. fio-s 4-6. 



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Table of Species of Ophiomitra. 



Nine rough, stout, solid arm spines. Disk evenly covered with large radial shields 1 



and scales, beset with thorny stumps, ] Ophiomitra valida. 



Six smooth, short, tapering arm spines. Upper disk bearing a few thorny stumps, ) 



and covered almost wholly by the large radial shields, . . . . J °P luomitra exigua. 



Four smooth, slender, solid arm spines. Disk sparsely granulated, . . . Ophiomitra normani. 



Five to six stout arm spines. Outer edge of under arm plate swollen, and in large ) 



specimens turned down, . . . . . . . ) Ophiomitra plicata. 



Eight arm spines, less stout than in preceding. Tentacle scales thorny, . . Ophiomitra sarsii. 



Six arm spines ; under one thickened or bent. Radial shields widely separated, . Ophiomitra chelys. 



Six arm spines ; the under one straight. Tentacle scales thorny. Under arm spine ) 



, . i , r Ophiomitra carduus. 



Six arm spines, the two uppermost very long and slender. Marginal disk plates large ) 



and much swollen. Central disk scales small, j Ophiomitra dipsacos. 



