PEDICELLARL-E. 663 



In the Cidaridae the pedicellariae are placed at the base of the circle of 

 the papillae surrounding the primary interambulacral spines ; they are more 

 numerous near the ambulacral areas. They are characterized by a shaft 

 made up of longitudinal rods, into the tip of which is set a second short cal- 

 careous rod, somewhat smaller in diameter than the shaft of the base (PL 

 XXIV. f. 5, 7). The longitudinal rods are soldered together by short irreg- 

 ular transverse processes. There are but few pedicellariae on the buccal 

 membrane, and frequently they are entirely wanting, while in the other 

 regular Echini the abactinal membrane is, at certain points, studded with 

 short-stemmed pedicellariae. The head of the pedicellariae of the interam- 

 bulacral pedicellariae are elongate (PI. XXIV. f. 7,11), toothed along the 

 edges, when they have reached their full size (PL XXIV. f. 2. 8, 8 a , 4), while 

 in the smaller stages the margins are nearly smooth (PL XXIV f. 1). The 

 young of these pedicellariae are quite solid and compact (PL XXIV. f. 9). 



There are found on the abactinal system of Dorocidaris and other genera 

 short-stemmed, stout-headed pedicellariae, much more delicate than those 

 just described (PL XXIV. f. 5, <?). The separate prongs of these short 

 pedicellariae are rectangular, with a pointed tip, a large open space at the 

 base of the prong, and the same transverse bar dividing the top into a dis- 

 tinct terminal triangular cavity (PI. XXIV. f. 0), as in the long-headed 

 pedicellariae (PL XXIV. f. 9). Below this bar there is an elongate cavity 

 with serrated edges; the very tip of the prong terminates in a hook (PL 

 XXIV. f. 8). 



In Goniocidaris, we find seated in the pits of the sutures of the interam- 

 bulacral and ambulacral median lines, a large, stoutdreaded, short-stemmed 

 pedicellaria (PI. XXIV. f. m, is), similar to those so numerous in the abac- 

 tinal system of other genera. 



In Porocidaris the long-headed pedicellariae are remarkable for the open- 

 ing near the base (PI. XXIV. f. 11). In the Diadematidae the large tridac- 

 tyle pedicellariae resemble somewhat those of the Echinidae proper ; they 

 differ in having few large marginal serrations (PL XXIV. f. 14, 87, 40); the 

 extremity of the prong is frequently spoon-shaped and widest at its very tip, 

 as in Asthenosoma. In the group of Echinothuriae occurs the only case of 

 pedicellariae with four prongs. Thomson has figured such pedicellariae in his 

 " Depths of the Sea " as found in Phormosoma. In Echinothrix the simi- 

 larity of the large, long-headed pedicellariae (PL XXIV f. 33 -36) to those of 

 Echinidae proper is very marked ; they differ, however, in the proportions 



