REPORT ON THE OPHIUROIDEA. 249 



muscle fields {w) and tentacle sockets (r). The outer face of the bone is one step nearer 

 Astfojjhyton than Opliiochondrus, having a large articulating shoulder (fig. 8, 4) without 

 any articulating peg below. The inner face (fig. 9) shows the simplest form of the 

 Ophiuran joint, and is largely occupied by the great umbo (l). In general, the position 

 of this highly interesting genus was correctly laid down by me in 1872.^ The original 

 discoverer, Von Martens,^ was, however, right in thinking it had a relationshijD, albeit 

 a faint one, with the Astrophytidse. 

 See Plate XLIIL figs. 7-10. 



Species of Hemleurijcde not herein described. 

 Hemieicri/ale pustitlata, V. Mart. (PI. XLIII. figs. 7-10). 



Hemieurijale imstidafa, Monatsb. Koiiig. Akad. Berlin, p. 48i, 18G7; Ljii., Dr. Goes, Oph. Of. 



Kong. Akad., p. 617; Lyni., Ann. Sci. Nat., vol. xvi., art. 4, p. .5; Bull. Mus. Comp. 



Zool., vol. iii., part 10, p. 268, jil. v. figs. 8-11. 

 Opliiiira cuspidiferaij), Lmk., Hist. Anim. sans Vert., vol. iii. p. 226, 2nd ed., 1840 ; Encycloped. 



Meth., pi. cxxii. figs. .5-8. 



West Indies ; 74 to 180 fathoms ; Senegal (?). 



Sigsbeia. 



Sigsheia, Lym., Bull Mus. Comp. Zool., vol. v., part 9, 1878. 



Disk small, covered with very large radial shields and heavy plates or scales, and 

 passing, without line of demarcation, into the stout arms, which can be rolled in a vertical 

 plane. Teeth and small close-set mouth papillae ; no tooth papUlse. Arms bearing the 

 usual plates, and in addition a large supplementary piece extending downward from the 

 upper arm plate. Two very small genital openings in each interlirachial space, near the 

 mouth shield. 



This singular genus forms a peculiar group with Hemieuryale, from which it 

 is distinguished by having ordinary upper arm plates, instead of a mosaic of small 

 pieces. 



It represents the maximum of lime deposit, both without and within. Nothing 

 can be more unexpected than the ease with which the animal rolls up Its arms incased 

 as they are in thick, clumsy armour, and having an axis of massive arm bones. The 

 radial shields are of great size and thickness, so that they cover nearly the whole upper 

 disk and form a connected circle (PI. XLIII. fig. 4, /). Attached to each is a short, 

 wide, thick, swollen, irregularly wedge-shaped genital plate (o), with a thick, narrow, 



1 Ann. Sci. Nat, vol. xvi. art. 4, p. 5. - Monatsb. Koni.L;. Akad. Berlin, p. 484, 1867. 



