270 PODOCIDAKIS SCULPT A. 



above the surface. The large primary spines are confined to the lower 

 surface as in Colobocentrotus, the primary tubercles scarcely extending beyond 

 the ambitus in the largest specimens obtained (PL IV. f. 9, 10). These tuber- 

 cles alone carry a large, smooth mamelon, while the rest of the test is covered 

 with rudimentary spines (PL IV. f. to), arranged, however, in regular, ver- 

 tical rows, four of which form a distinct, raised band in the median interam- 

 bulacral zone, flanked by three more, less well defined, placed in a compara- 

 tively lower plane, while in the narrow ambulacra] /one there are but two 

 such rows, close to the poriferous zone, which is very narrow, the pores being 

 arranged in a single vertical row, as in Arbacia (PL IV. f. 1 >). The rudimen- 

 i.ii v. knob-shaped spines,* strongly serrate, are not carried upon a mamelon, 

 but rise directly from the test, as in very young Sea-urchins, and are con- 

 nected at their base by a ridge, leaving thus a more or less quadrangular 

 pit in the space between four tubercles {PI. IV. f. 13). This ridge is par- 

 ticularly prominent between the spines of the median interambulacral 

 rows, while in the more irregular rows the ridges are less marked, form- 

 ing simply depressions in the test, running irregularly. The pits in the 

 ambulacra] zone are very marked, and are connected into an irregular 

 groove extending along the whole ambulacra! zone, the ridges, starting 

 from the base of the tubercles, extending only part way across the am- 

 bulacra! area, like spurs and rounded knobs. The whole surface of the test 

 (PL IV. f. 8) is covered with long-stemmed, articulated pedicellarire (PL IV. 

 f. li;). which have a distinct mamelon for their support (PL IV. f. /■/). sur- 

 rounded by a sort of scrobicular circle, the base of the pedicellarise forming 

 a ball-and-socket joint with the tubercle, while there is a thin muscular mem- 

 brane holding them in place, as in true spines, — an additional proof that 

 pedicellarise are only modified spines, as was made probable by their identical 

 mode of development with spines, observed in the Starfishes and Spatangoids 



* We have in the adult of this genus, occurring with articulated spines such as are found in fully 

 grown Echini, rudimentary spines rising directly from the test, as we find them in very young Echini or in 

 all Starfishes, yet associated with pedicellarisB having an articulation playing upon a distinct tubercle, and 

 surrounded by a scrobicular circle. The probable function of the pedicellarise of scavengers and providers 



seems tolerably well proved, not only by my own observations in our common Sc -a-urehin, hut also by those 

 of other writers on the pedicellarise of other genera, when- they have been seen c'asping small Crustacea, 

 Annelids, and other minute marine animals. Starting from the simple network of the reticulation of the 

 test, we pass gradually to all the forms of spines, whether fixed or articulated, whether appearing as mere 

 knobs or granules, to the complicated articulated spines of Cidaris on one side, or from the same granules 

 through fixed pedicellaria? to the highly articulated and movable pedicellaria? of this genus. To this 1 shall 

 recur again when describing the pedicellaria; of Echini in connection with other anatomical points. 



