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



Fio-. G. 0'pMomyccsfniiectosus,'Lym., \o. Disk and base of an arm seeu diagonal]}' from 



above, showing the large genital openings, 

 with their wide, thin plates (o) and scales 

 (»). The disk scaling is uniform showing- 

 no radial shields ; arm spines {p). 

 7. jj ,, \". Skeleton of the base of an arm, with a mouth 



angle. A piece of the disk roof is turned 

 up to show its under side, which ex- 

 hibits no trace of radial shields. This 

 lack is almost unicjue among Ophiurans. 

 The very wide, thin genital plates (o) are 

 striated lengthwise, wliich shows that 

 they are built up like arm spines, and are 

 not composed of soldered plates. 



,, 8. ,, „ Y'- Outer face of an arm bone which is pecu- 



liar in its simplicity, and in lacking the 

 articulating peg. 



,, 9. ,, „ ij'^. Inner fece of an arm bone, with its pecu- 



liar umbo (l). 



,, 10. AstrofjompJius rallatiis, Lym., f . A genital plate (o) and radial shield {!) in 



profile showing that the latter is composed 

 j)artly of soldered scales, as in Gorgonoce- 

 2^halus. 



„ 11. ,, „ f. A portion of skin from back of disk, seen from 



back of disk, seen from the inside, with a 

 pair of radial shields (/), and the mosaic 

 of the skin, the central part of which is 

 curled up showing some of the spikes. 



„ 12. „ „ -f. Skeleton of a mouth angle from above. 



Next the peristomial plate (r) is the angle 

 piece. The mouth frames {_/) are like 

 those of Astroschema, and approach also 

 those of Ophioscolex. 



,, i3» Hemipholis cmxlifera, Lym., Y'- (Figs. 13 to 16 are from drawings by the late 



Professor H. J. Clark, made in Charleston, 

 S. C, in 1852, when an assistant of 

 Professor Agassiz.) Mouth and one angle 

 of the disk of a living specimen : mouth 

 shield (rt), side mouth shield (/>), jaw (c), jaw 



