386 THE VOYAGE OF H.M.S. CHALLENGEE. 



is, in the most backward of the brood, 0"5 mm., while in the most advanced it equals the 

 diameter of the test. The peri some, in which the cribriform rudiments of the plates of 

 the corona and the young spines are being developed, is loaded with dark purple pigment, 

 which makes it difficult to observe the growth of the calcareous elements. About thirty 

 primary spines arise on the surface of the corona almost simultaneously in ten rows of 

 throe each: they first make their appearance as small papillae covered with a densely 

 pigmented ciliated membrane ; and when they have once begun to lengthen, they run 

 out very rapidly until they bear to the young nearly the same proportions which the 

 full-grown spines bear to the mature corona. Very shortly some of the secondary spines, 

 at first nearly as large as the sprouting primary spines, make their appearance in the 

 interstices between these ; and a crowd of very small spines rises on the nascent scales of 

 the peristome. Successively five or six pedicellarise are developed towards the outer 

 edge of the apical area, which at this stage is disproportionately large ; the pedicellariaa 

 commence as purple papillae, which are at first undistinguishable from young primary 

 spines ; the first set look enormously large in proportion to the other appendages of the 

 perisome. Almost simultaneously with the first appearance of the primary spines, ten 

 tentacular feet, apparently the first pairs on each ambulacrum of the corona, just beyond 

 the edge of the peristome, come into play; they are very delicate and extremely extensile, 

 with well-defined sucking-disks ; and with these the young cling to and move over the 

 spines of the mother, and cling to the sides of the glass vessel, if they are dislodged from 

 the marsupium. This species seems to acquire its full size during a single season. We 

 dredged it at the close of the breeding season, and took no specimens intermediate in 

 size between the adult and the young. 



" Among the marine animals which we dredged from the steam pinnace on the 19th 

 of January 1874, at depths of from 50 to 70 fathoms in Balfour Bay (a fine recess of one 

 of the many channels which separate the forelands and islands at the head of Royal 

 Sound, Kerguelen Island), there were several examples of a small Cidaris, which I will 

 name provisionally Cidaris nutrix 1 (fig. 142). 



" This species resembles Cidaris papillata in the general form and arrangement of 

 the plates of the corona, in the form and arrangement of the primary tubercles of the 

 interambulacral areas and of the secondary tubercles over the general surface of the test, 

 in the form of the plates of the apical disk and of the imbricated calcareous scales of the 

 peristome, in the form, sculpture, and proportionate length of the primary spines, and in 

 the form of the different elements of the jaw-pyramid and in that of the teeth ; but the 

 test is more depressed, the secondary spines which articulate to the ambulacral plates and 

 cover the pore-areas are longer and more cylindrical, not so much flattened as they are in 

 Cidans papillata ; the large tulip-like pedicellarise and the long thin tridactyle pedicel- 

 lariae mixed with the secondary spines in the northern species are wanting, or in very 



1 Described by Alex. Agassiz as a variety of Goniocidaris canaliculuta, Zool. Chall. Exp., part ix., p. 44, 1881. 



