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



with numerous short conical spines and one longer terminal spine. (Resembles Stauralastrum- 

 rhopalophorum, PI. 45, fig. 1, but with six rays instead of four.) 



Dimensions. Eadius of each arm 0'3, basal breadth 0'03, distal breadth 0'08. 



Habitat. Pacific, central area, Station 268, depth 2900 fathoms. 



Subgenus Hexalastromma, Haeckel. 

 Definition. Arms more or less different in size or form ; shell bilateral. 



3. Hexalastrum orchidaceum, n. sp. (PI. 44, fig. 5). 



Hexactura orchidacea, Haeckel, 1881, Prodromus, p. 459. 



Arms different in length, so that two unequal opposite odd arms determine the main axis, 

 and the four other arms lie on both sides of this as two different pairs. The proportion of their 

 relative length is the following: anterior lateral arms five, anterior odd arm six; posterior lateral 

 arms seven, posterior odd arm eight. Each arm is club-shaped, two to three times as long as broad, 

 and divided into six to eight joints by five to seven transverse septa ; its distal end is armed with a 

 terminal spine and twice as broad as its base. 



Dimensions. Eadius of the posterior odd arm 0'4, of the anterior odd arm 0'3 ; of the posterior 

 lateral pair 0'35, of the anterior lateral pair 0'25 ; basal breadth 0'08, distal breadth 0'16. 



Habitat. Pacific, central area, Station 266, depth 2750 fathoms. 



Genus 244. Hexinastrum, 1 Haeckel, 1881, Prodromus, p. 461. 



Definition. P orodiscida with six simple, undivided, chambered arms, con- 

 nected by a patagium. 



The genus Hexinastrum differs from its ancestral form Hexalastrum by the 

 development of a patagium between the arms. The only observed species is regular. 



1. Hexinastrum geryonidum, n. sp. (PI. 44, fig. 4). 



Hexalastrum geryonidum, Haeckel, 1879, Atlas (pi. xliv. fig. 4). 



Disk quite regular with six radii ; all six arms of the same size and form, at their broad, convexly 

 rounded, smooth end five times as broad as at their narrow base, and little longer than broad. Each 

 arm is divided by eight transverse septa into nine simple joints or chambers of the same height ; 

 the breadth of the distal chambers increases rapidly. The regular, hexagonal, central disk exhibits 

 four concentric rings around the central chamber. Patagium between the arms incomplete, witli 

 concavely fluted edge. 



Dimensions. Eadius of each arm 0'15, basal breadth O'OIG, distal breadth 0'08 ; radius of the 

 central disk 0'04. 



Habitat. Pacific, central area, Station 272, depth 2600 fathoms. 



1 Hexinastntm = Stamik-t with six rays ; t'^a., '/i/of, awr(;o. 



