ISOMETRINAE i8i 



segments of the other oral pinnules are attached to the arm by a web of tissue. Pg is of 

 9-13, usually 10, segments and 5-7 mm. long. P3 is of 9-14, usually 10-12, segments 

 and 4-7 mm. long. 



The first genital pinnule is P4 , P5 or P^ , usually P5 . The last may be so far out as 

 P26, or perhaps farther. The genital pinnules (Fig. 15 J, e) are about 10 mm. long and 

 are usually of 16-19, ^ut exceptionally of up to 24, segments. The distal pinnules are a 

 little shorter and of slightly fewer segments. 



Mortensen (1920, p. 32) found as many as eight eggs and embryos in one brood- 

 pouch. That there are much larger numbers in the females of this collection may be 

 seen without dissection or preparation, but one brood-pouch of each of three specimens 

 was examined. The first contained ten eggs and three young embryos; the second, eight 

 eggs and eleven embryos of all ages; the third, six eggs and twenty-one embryos of all 

 ages. The oldest embryos are more fully developed than Mortensen 's "full-grown 

 larvae" (1920, pi. xxii, figs. 6-8) for the oral and basal plates are in contact with one 

 another and reach to near both poles ; these larvae appear almost completely mail-clad. 



A distal pinnule of each of 16 specimens, including two that were immature, was 

 examined. The ambulacral skeleton is usually as Mortensen describes it (1918, p. 13, 

 fig. 12, pi. ii, fig. 5). In four specimens, three mature and one immature, the side- and 

 cover-plates are better developed and the latter are of the bush-like form of those of 

 /. lineata. They are best developed in one of the mature specimens (Fig. 15/). Spicules 

 may be very abundant in the tentacles. 



In all the specimens in which the disk can be seen it is naked. 



Six of the twelve more complete females carry small numbers of pentacrinoids on 

 their cirri. 



The single specimen from the Bransfield Strait (St. 175), which is a female with arms 

 over 50 mm. long, is somewhat different, (i) On all the arms P3 is the first genital 

 pinnule and P13 the last; the distal pinnules are of 15-17 segments and about 8 mm. 

 long, (ii) The most expanded segments, the third to the fifth, of the middle genital 

 pinnules are not so wide as those of females from the Falklands and the Burdwood 

 Bank (Fig. 15^). The brood-pouches contain many fewer eggs and embryos. The con- 

 tents of two were examined : in each there were three embryos and one egg. In one the 

 embryos were as large and as well developed as those described above, (iii) The position 

 of the second syzygy is abnormal : on eight of the arms it is between the eleventh and 

 twelfth, on one between the sixth and seventh, and on the other between the twelfth and 

 thirteenth brachials, (iv) The side- and cover-plates of the pinnule ambulacra are well- 

 developed : the side-plates are plate- not rod-like. There are few spicules in the tentacles. 



Pi , of about 12 segments and over 5 mm. long, is slightly longer but not stouter than 

 P2 which is of about 10 segments and 5 mm. long. The outer brachials and pinnulars 

 have finely thorny distal edges. 



