OF THE CIDARID.E. 571 



form pedicellarise of the Echinidae, and which, in them probably serves as a channel for 

 the injection of a poison secreted by two sac-like glands appended to each jaw-like piece 

 of the pedicellarian head. It wonld appear from this that the armed pedicellarise of the 

 Cidaridse are the analogues of the gemmiform ones of the Echinidse. The position of the 

 opening in the fang is admirably adapted for the injecting of poison into a wound; 

 the flesh, which is compressed on its inner or convex side, has a cavity torn in it in 

 front, into which the poison could readily pass, from the opening of the fang being 

 situated in its anterior border and not at its point. A similar contrivance for a like 

 purpose is found in the falces of spiders, poison-fangs of most venomous snakes, &c. 



Mixed with the ordinary forms of pedicellarise on or near the apical system of 

 D. papillata, I have often found the large armed variety possessing four jaws; this is, 

 I believe, the second instance of such an exception to the rule of there being three only, 

 a very remarkable form having been previously described by Sir Wyville Thomson as 

 existing in Asthenosoma. It differs, however, in all other respects from those of the 

 latter genus, only varying in the number of its jaws from the ordinary form found in 

 Doricidaris. 



The next point to which I wish to call attention is that in Cidaris tribuloides and 

 JPhyllacanthus bacidosa, in addition to the minute calcareous arches which bridge over 

 the first three or four of the inner ambulacral pores, counting from the inferior opening 

 of the corona, and which have already been described by J. Muller under the name 

 of vertebral processes, there are between all the inner pores delicate solid spines, some- 

 times two in number, between each pair of pores ; they project downwards, and tend to 

 arch over the ambulacral vessel. The vertebral processes, of which these spines are 

 but a modification, have already been shown, in the paper by J. Muller before 

 referred to, to be the homologues of the auriculae of the Diadematidse, Echino- 

 metradse, and Echinidae, and of the vertebral ossicles of the Asteroidea, which 

 in like manner arch over the ambulacral vessel and nerve. The continuation of the 

 representatives of these arches throughout the whole length of the ambulacra in some 

 of the Cidaridse becomes therefore interesting. These spines remind one of similar pro- 

 cesses scattered over the inner surface of the corona in the Clypeastridae. 



The genital gland of D. papillata shows a spicular framework consisting of calcareous 

 triradiate spicula, some of which are of large size, and have their angles more or less 

 filled by an irregular network ; occasionally also one of the radii is prolonged, and projects 

 as a spine from the surface of the gland. Sir Wyville Thomson, in his ' Voyage of the 

 Challenger,' vol. ii. pp. 227, 228, describes an interesting new species of Cidaris under 

 the name of C. nutrix. He points out many features of resemblance presented by it 

 to D. papillata, and others in which it differs from that species, amongst which is men- 

 tioned the paucity of spicula in the walls of its genital glands, whereas D. papillata is 

 said to have them in great abundance. Having examined a considerable number of 

 the latter species, I find great variation in the number of the spicula, although their 

 general form is constant in similar specimens, those having comparatively small genital 

 tubules having the spicula most abundant, whereas where the tubules are of large size 

 (females ?) the spicula are often very scanty and small. 



