42 THE VOYAGE OF H.M.S. CHALLENGER. 



from the Mediterranean, one primary tubercle ou the equatorial part of the test showing 

 most distinct traces of crenulation. 



I have not found crenulated tubercles in any of the species of Goniocidaris I 

 have thus far examined {Goniocidaris tubaria, Goniocidaris geranioides). In all the 

 specimens of Dorocidaris I have thus far examined, the -tubercles were all smooth, with 

 the exception of an occasional pit, which may prove to be the first indication of a more 

 definite crenulation in the genus. Even in Dorocidaris blakii (Alexander Agassiz, Bull. 

 Mus. Comp. Zoo]., 1879) no trace of crenulation has been found in any of the specimens 

 I have examined. Yet this species, from its remarkable radioles alone, would, if found 

 fossil, have been referred to Rhahdocidaris without any hesitation by every paleeon- 

 tologist. 



I hope, in the examination of the series of Dorocidaris blakii for the final Report of 

 the Echinids of the " Blake," to have some additional data on this subject, and to enter 

 again into an examination of the crenulation of the tubercles in the other families of 

 recent Echinids in which this character is found, more particularly in the Clypeastroids 

 and Spatangoids, where the crenulation of the primary tubercles is not uncommon in 

 many species on some part of the test. 



The mammary boss is prominent and perforate. There are not in either of the 

 denuded specimens of this collection any traces of the muscular impressions ou the areola 

 on which Desor characterised the genus, and which, as Thomson has already shown, is not 

 an important feature, being frequently greatly developed in other genera, and depending 

 on the strength of the muscular attachment of the spines. This species and Porocidaris 

 purpiirata difier in the position of the genital openings. In the present species, in a 

 specimen measuring 41 mm. in diameter, the female openings are large (PI. III. fig. 2), 

 circular, and entirely within the genital plates ; and do not extend, as in Porocidaris 

 purpurata, into the interambulacral area. The large female genital openings probably 

 indicate that Porocidaris elegans, like Goniocidaris canaliculata, is viviparous. 



Thomson has described in an alcoholic specimen of Porocidaris pur^mrata the large 

 eggs and ovaries, which resemble those of other viviparous species of Cidaris. The 

 position of the genital openings in some of the Cidaridae (as in Goniocidaris) encroaching 

 upon the interambulacral system is interesting, as indicating the first trace of the separa- 

 tion of the genital openings from the apical system. Such an absence of connection, or 

 so indifferent a connection between the so-called genital plates and the apical system, 

 occurs in many groups of Echinids. This connection becomes entirely severed in some 

 species of Clypeastroids. The ocular plates are broader than in Porocidaris purpurata. 

 In a younger specimen measuring 28 mm. in diameter (PI. III. fig. 4) the genital 

 openings were quite small. This specimen may be only a male, or the genital openings 

 may be developed to their full size much later. It is more probable, however, that this 

 example is a young male. 



