ASTEROIDEA 131 



with the " Stellosphcera mirabilis ". The fact that this Brachiolaria 

 hibernica was found 50 miles W. of Ireland would then indicate 

 that Pedicellaster sexradiatus does occur in the British seas. 



II. Family Zoroasterid.^ 



Rays 5, long and slender, stiff, tapering ; not restricted at 

 base and not sharply defined against the small disk. Dorsal 

 skeleton larger plates arranged in regular longitudinal series, 

 generally covered with small spines. The series of plates along 

 the mid-line of arms, the " carinals ", especially prominent, often 

 with a conspicuous spine. Disk with a fairly conspicuous rosette 

 of larger plates. Adambulacral plates mostly of two alternating 

 sorts, one projecting into the furrow as a vertical keel, the other 

 retracting, not keeled. A projecting plate on one side of the 

 furrow corresponds to a retracting plate on the other side. 

 Tube-feet mostly with only a smaU sucking disk, generally only 

 in two series in the distal part of arm, mostly in four series in the 

 proximal part. Straight pedicellariae usually present ; no crossed 

 pedicellariae. 



Only one genus, Zoroaster Wyv. Thomson, has been recorded 

 from the British seas, but very probably also the second genus of 

 the family known from European seas, Prognaster E. Perrier, will 

 prove to occur there ; the single species (and only specimen 

 known) of this genus, Prognaster Grimaldii E. Perrier, was found 

 at 41° 40' N., 29° 04' W., 2870 m. (" Hirondelle "). 



Key to the genera of ZoroasteridcE known from or likely to 



occur in the British seas. 



All the adambulacrals projecting into the ambulacral furrow, and 



with a vertical keel .... Prognaster Perrier 



Only every second adambulacral projecting into the furrow, and 



with a vertical keel . . 1. Zoroaster Wyv.. Thomson 



1. Zoroaster Wyv. Thomson. 



Plates of arms arranged in distinct, regular, longitudinal 

 rows ; they are covered with skin-clad spinelets, and most of 

 them bear an enlarged spine. Ventro- lateral plates in three to 

 five series ; lower and upper marginals about equal sized. 

 Straight pedicellariae present. Mouth very deep. Sucking disk 

 of tube-feet small. 



Only one species known from British seas, but another, 

 Zoroaster longicauda (Perrier) (Syn. Prognaster longicauda 

 Perrier), is likely to occur there also (known from Bay of Biscay, 

 Azores, Cape Verde, ca. 1260-4250 m.). 



