2i6 DISCOVERY REPORTS 



it quite beyond doubt that Bernard's observation rests on a misinterpretation, viz. that 

 the young specimen (of 6 mm. h.d.) which he found on the peristome of one of his 

 specimens had come there accidentally, probably during capture or preservation. The 

 fact that the eggs of A. Diifresnii are very small, o-i mm., and extremely numerous 

 is entirely incompatible with a brood-protecting habit and indicates that this species has 

 pelagic larvae, as is the case with the other species of Arbacia. Studer's observation 

 {GazeUe-EcJiinoidea, Monatsber. Akad. Berlin, 1880, p. 868) that the eggs when shed 

 remained attached to the test, is no doubt due to the unnatural conditions under which 

 the observation was made. In any Echinoid with pelagic larvae the same thing may be 

 observed ; ripe specimens on being removed from the water are very often induced to 

 shed their eggs and then the eggs will remain in thick clusters on the test, among the 

 spines, whereas when shed under natural conditions the eggs are gradually dispersed in 

 the water. I have found such thick layers of eggs in preserved specimens of many 

 species of sea-urchins known to have pelagic larvae ; and not only the eggs, even the 

 sperm may be found similarly lying in thick layers on the test. Both cases are found 

 among the specimens of ^. Diifresnii in this collection. It may be added that these eggs 

 — as was to be expected — are found to be unfertilized, or at least cleavage has not yet 

 begun. We may thus certainly dismiss, as without any foundation whatever, the idea 

 that A. Diifresnii is a brood-protecting species (cf. Mortensen, Swedish South Polar 

 Exped. Echinoidea, p. 32). 



Family DIADEMATIDAE 

 Diadema antillarum, var. ascensionis, Mortensen 



Diadema ascensionis, Mortensen, 1909. Deutsche Siidpolar-Exped. Echinoiden, p. 55, Taf. vii, 



fig. 10; xvi, figs. I, 4, 8, 16-17, 21-23. 

 D. antillarum, var. ascensionis, Mortensen, 1933. Eclmioderms of St Helena (other than Crinoids). 



Papers from Dr Th. Mortensen 's Pacific Exped., 1914-16, Lxvi (Vid. Medd. Dansk Naturh. 



Foren., 93), p. 465. 



For other literary references see my paper of 1933, loc. cit. 

 St. I. 16. xi. 25. Clarence Bay, Ascension, 16-27 "i- 7 specimens. 



As set forth in my paper on the Echinoderms of St Helena, the shape of the tridentate 

 pedicellariae is so characteristic and constant that it is not justifiable to identify this 

 mid- Atlantic Diadema simply as D. antillarum. Whether we regard it as a variety of the 

 latter, or as a separate species, is of small importance. 



The specimens all have the spines banded with white and brownish, and are, indeed, 

 very delicate and beautiful objects. Concerning the blue lines (which appear white in 

 the preserved specimens) it may be pointed out that there are two parallel lines in each 

 interambulacrum, not one bifurcating line, as stated in my paper on the St Helena 

 Echinoderms ; the two lines issue separately from the apical ring, though apparently not 

 directly connected with the latter. 



