CIDARIDAE 211 



mens may already have genital openings at a size of ca. 12 mm. h.d. The test may be 

 much more flattened in the parasitized than in the normal specimens. Further, it is a 

 natural consequence of the smaller size of the primary spines that the primary tubercles 

 and their areoles are on the whole conspicuously smaller than in the normal specimens, 

 and while in the latter they are, in the larger specimens, confluent to a considerable 

 extent, they are in the parasitized specimens less confluent, sometimes even con- 

 spicuously apart. The median interambulacral space is also, of course, correspondingly 

 more developed than in normal specimens (compare Plate I, fig. 7 with fig. 6). Further, 

 the pedicellariae may aff'ord a curious difference in being invested with a much thicker 

 skin than in normal specimens (cf. Swedish South Polar Exped. Echinoidea, p. 10); 

 this, however, is not a constant feature. 



I may recall here the fact that Ctenocidaris Perrieri, Koehler, is also liable to attack by 

 the parasite Echi?iop/iyces (cf. Monogr. Echinoidea. I, Cidaridae, p. 124). 



The specimens from Sts. 170 and WS 42 differ from the typical form in having the 

 oral primaries more spade-shaped, without coarse serrations (compare Plate I, figs. 3 

 and 5). As, however, they do not differ in their other characters from the typical form, 

 and as also specimens intermediate in this regard occur, there is no reason for dis- 

 tinguishing these specimens as a separate variety, still less as a separate species. 



In the original description of this species {op. cit., p. 7) it was suggested that it might 

 prove to be brood-protecting. In the material at hand there are, as a matter of fact, 

 some specimens which carry embryos on the peristome — but only among the parasitized 

 specimens ; not one of the several normal adults is carrying young ones. Does it mean, 

 perhaps, that only the parasitized specimens are brood-protecting, the normal ones not.? 

 This question cannot be answered from the material at hand. In the quite young, 

 normal specimens, ca. 3 mm. diameter of test, the primary spines are of a distinctly 

 embryonal character, rather strongly thorny (cf. Swedish South Polar Exped. 

 Echinoidea, pi. xiii, fig. 6), very different from the largest of the embryos found in the 

 marsupium of parasitized specimens ; also the youngest free parasitized specimens have 

 their primary spines much less thorny, and in addition their secondary spines differ 

 from those of the normal ones in being coarser. 



Ctenocidaris Perrieri, Koehler 



Ctenocidaris Perrieri, Koehler, 1912. 11^ Exped. Antarct. Franfaise. Echinodermes, p. 150, 



pis. xii, figs. 4-8; xiii, figs. 2-8; xiv, figs. 9-14; xv, figs. i-io. 

 C. Perrieri, H. L. Clark, 1925. Cat. Recent Sea-Urchins Brit. Mus., p. 35. 

 C. Perrieri, Mortensen, 1928. Monogr. Echinoidea. I, Cidaridae, p. 123, pi. Ixix, fig. 23. 

 St. 181. 12. iii. 27. Schollaert Channel, Palmer Archipelago (64° 20' S, 63° 01' W, 160-335 ™-)- 

 4 adult specimens and i very young specimen. 



None of these specimens carry embryos on their peristome, and there is thus still no 

 proof of the suggestion set forth in my Cidarid Monograph {op. cit., p. 124) that this 

 species may be brood-protecting like C. speciosa. All the specimens are normal, not 

 infested with Echinophyces. 



