174 DISCOVERY REPORTS 



into a row of strong spines, much longer than those of Phrixornetra mitrix. The 

 brachials between the first and second syzygies are roughly rectangular, about as long 

 as broad (Fig. 12 c); the distal are elongated, roughly oblong (Fig. 12 d). Syzygies are 

 numerous, the first between the third and fourth brachials, the second between the 

 ninth and tenth and the third between the fourteenth and fifteenth; beyond the third 

 the syzygial pairs occur at intervals of only one brachial. 



In all pinnules the first segment is short, the second as long as or a little longer than 

 broad. The remainder are elongated and somewhat constricted in the middle, the 

 proximal less so than the distal ; the distal edge of each is produced into a wide spiny 

 flare around the base of the next, giving the joints a swollen appearance (Fig. 12 e). 

 Pi is of II or 12 segments, ca. 3 mm. long; P.^ of about 13 or 14 segments, ca. 4 mm. 

 long, with no gonad. P3 is the first genital pinnule ; it is shorter than Pg , of about 9 

 segments, en. 3 mm. long. There are only three pairs of genital pinnules, all resembling 

 Pg . The long yellow gonad lies along the third to sixth segments. Pg is the first to have 

 an ambulacral furrow. The outer pinnules are of up to 14 or 15 segments, 4-5 mm. 

 long. 



The disk cannot be seen. The anal cone appears to be high. 



The sacculi are fairly conspicuous, irregularly arranged along the genital pinnules, 

 regularly along the outer. 



There are no side- and cover-plates along the ambulacra of the outer pinnules nor 

 any spicules in the tentacles. 



The colour in spirit is whitish, the gonads a pale yellow. 



I hesitated for a long time before describing this specimen as a species distinct from 

 niitrix which it so strongly resembles. The cirri of the two species are similar and so are 

 the pinnules, except that the oral pinnules of this species are more rigid and spiny. The 

 species is altogether more spiny than mitrix. P3 is the first genital pinnule, not P2 as in 

 nutrix. 



What makes me describe it as a new species is that it has only 30 cirri whereas 

 Mortensen's female specimen of nutrix and my male have 45. 



Subfamily ISOMETRINAE 



Genus Isometra A. H. Clark 



Clark (1908, p. 133) formed this genus with A?itedon lineata Carpenter 1888 as 

 genotype and Isometra angiistipinna (Carpenter) as the only known species. He wrote: 

 "Isometra angustipinna is without doubt the young of Antedon lineata. Carpenter." 

 Carpenter's species A. lineata and A. angustipinna were each described from one speci- 

 men taken at the same Challenger station off^ the mouth of the River Plate, the depth 

 being 1097 m. Neither has since been recorded. As thorough an examination as their 

 frail condition would allow has been made of the two specimens. Each is mature and 



