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



spines. The diameter of the central disk is larger than the length of the arms. The angles between 

 the arms are equal and filled up by an incomplete patagium, so that the whole disk forms a regular 

 pentagon with five concave sides. 



Dimensions. Eadius of each arm (without terminal spine) 014 ; breadth at their base 0'02, at 

 their terminal joint 0'03 ; radius of the central disk 0'06. 



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



2. Pentinastrum goniaster, n. sp. 



? Stephanastrum sp., Bury, 1862, Polycystins of Barbados, pi. xx. fig. 1. 



All five arms equal, four times as long as broad, club-shaped, at their globose distal end twice as 

 broad as at their base, and armed with a strong conical terminal spine. Diameter of the central 

 disk equals only one-third of the length of the arms. The articulation of the spongy arms is 

 somewhat obscure. Patagium complete, totally fills up the interbrachial spaces, so that the whole 

 disk forms a regular pentagon with five rectilinear sides, except that the terminal spines project at 

 the corners. 



Dimensions. Radius of each arm 018, basal breadth 0'02, distal breadth 0'04 ; radius of the 

 central disk 0'05. 



Habitat. South Pacific, Station 295, depth 1500 fathoms ; also fossil in the rocks of Barbados. 



Genus 242. Pentophiastrum, 1 n. gen. 

 Definition. P orodiscida with five forked chambered arms, without a patagium. 



The genus Pentophiastrum differs from the two preceding genera by the bifurcation 

 of the five arms, and can be derived either from Pentalastrum by the ramification of the 

 distal ends of the arms, or from the similar Myelastrum by the increase in the number 

 of arms. 



1. Pentophiastrum dicranastrum, n. sp. 



All five arms equal, with equal angles between them. Each arm in the basal half simple, in 

 the distal half forked ; both branches of it equal, with obtuse ends. (This regular species resembles 

 Dicranastrum furcatum, PL 47, fig. 2, but with five rays instead of four ; also the form of the 

 arms is more slender and the edges smooth.) 



Dimensions. Radius of each arm 0'25, breadth 0'05. 



Habitat. Equatorial Atlantic, Station 347, depth 2250 fathoms. 



Subgenus Pentophiastromma, Haeckel. 



Definition. Arms of different size, one odd arm opposite to the angle between 

 both arm-pairs. 



1 Pentophiastrum =Starrulet with five snakes ; vim, citfis, 



