ASTEROIDEA 



61 



This form is so very closely related to Psilaster that it may 

 well be regarded as doubtful whether it really deserves to rank 

 as a sej^arate genus or j^erhaps rather 

 should be united with Psilaster. 



The elongate median furrow spine 

 is very brittle and very often is lost, 

 more or less completely, in preserved 

 specimens. Sometimes the broken 

 point hangs, by means of the en- 

 closing skin, as a small flag on the 

 basal part of the spine. Such broken 

 spines were at first mistaken as re- 

 presenting a special structure peculiar 

 to this sea-star, designated as the 

 "vexillum", and gave rise to the 



species name vexillifer. It has also 



, 1 . > . 1 1-1 Fig. 34. — Side view of adam- 



been wrongly mterpreted as a kmd bulacral plate, with the 



of pedicellaria. furrow spines, of Bathy- 



r^ ^ • £ A • i-i, hiaster vexillifer. (From 



Only one species found m the Th.Mortensen,A^.£. Green- 

 North Atlantic, land Echinoderms.) x 22. 



1. Bathybiaster vexiUifer {Wyv. Thomson). (Fig. 35.) 



(Syn. Archaster vexillifer Wyv. Thomson ; Arckaster rohiistus 

 Verrill ; Bathybiaster pallidus Dan. and Koren ; Bathybi- 

 aster robustus (Verrill) ; Ily aster mirabilis Dan. and Koren ; 

 Phoxaster j^umilus Sladen.) 



The sides of the arms vertical, formed by the very high and 

 narrow marginal plates, which are wholly covered by short, flat, 

 scale-like spines. Generally there is a short conical spine at the 

 upper edge of the upper marginal plates, often wanting, however, 

 in those at the base of the arms and along the interradii. The 

 lower marginal plates generally have a somewhat longer and more 

 slender spine at the lower edge, and often two-three more, placed 

 irregularly higher up on the plate. Adambulacral plates rather 

 strongh^ projecting into the wide ambulaeral groove, the tri- 

 angular projection being emphasised through the enlarged median 

 spine. Paxillse of the dorsal side rather large, more or less dis- 

 tinctly arranged in transverse series along the sides in the basal 

 part of rays. R = ca. 4-6 r. Colour in life pale yellow or pale rose. 



Grows to a size of ca. 13 cm. R. The young specimens have 

 a distinct dorsal conical prominence. Biology and development 

 unknown. 



