REPOET ON THE HEXACTINELLIDA. . 121 



(Walzensterne). Short strong prickles, usually three at each extremity, diverge from 

 both ends, and frequently also from the middle of a somewhat thick, straight, or slightly 

 bent roller-like body. I regard these roller stars as reduced oxyhexasters, in which only 

 one axis, with the two princijial rays and the associated terminals, has attained full 

 development, while the other four rays arc either entirely atrophied, or are reduced to 

 short transverse prickles (PI. XXII. fig. 7, a, h, c). 



The dermal skeleton consists of simple, moderately strong, pentact hypodermalia and 

 pentact autodermalia in the form of pinuli. In the latter the fir-tree-like distal ray, which 

 measures 0"1 mm. in length, is naked at the base, broadest in the middle, and runs out 

 to a point superiorly, while the four transverse rays lying in the dermal membrane bear 

 on their larger outer portion small points and irregularities. A small, rounded, smooth 

 peg appears in the place of the atrophied proximal ray (PI. XXII. fig. 8). 



The simple pentact hypogastralia completely resemble the hypodermalia, nor do the 

 inwardly projecting gastralia differ much from the corresponding (inwardly projecting) 

 dermalia. These are very long, outwardly bent, slender hexacts, in which the narrow 

 pointed proximal ray which projects freely into the gastral cavity is beset only with 

 short prongs, which run obliquely outwards and attain a length of 0'5 mm. or more, 

 while the similarly armed pointed distal, which projects into the parenchyma, measures 

 only 0'17 mm. in length, and the similarly formed four cruciate transverse rays, are only 

 about O-I mm. long (PI. XXII. figs. 5, 9). 



The stalk exhibits the same general structure as the body, except that the hexact 

 principalia fall into the background as compared with the extraordinarily prolonged 

 diacts, which are all arranged parallel to the long axis, and which, as Oscar Schmidt 

 accurately describes,^ are firmly united laterally by numerous synapticula. The 

 size of the hjqpodermalia decreases downwards, and they are, moreover, pronged and 

 rough. 



Discohexasters, plumicomes, and "roller stars" may be found in the sto.lk in almost 

 as great abundance as in the body. 



Genus 2. Polyrhabdus, n. gen. 

 The genus contains only the one species, Poli/rhahdus oviformis. 



Polyrhabdus oviformis, n. sp. (PI. XXIII. figs. 1-8). 



In the Antarctic Ocean (lat. 62° 2G' S., long. 95° 44' E.) there was trawled from a depth 

 of 1975 fathoms, and a bottom of Diatom ooze, the considerably damaged and triturated 

 egg-shaped specimen represented in PI. XXIII. fig. 1. It measures 2 cm. in length and 



■ Loc. cit., pi. i. figs. 10-12. 



(ZOOL. CHALL. ESP. — PART LIU. — 1880.) Ggg 16 



