REPORT ON THE ECHINOIDEA MORTENSEN 289 



median line. On the adradial side of the scrobicular ring also there 

 are several miliary tubercles, the scrobicular tubercles not coming 

 very close to the edge. The median part is about half the width of 

 an areole, scarcely at all sunken toward the mid line. 



The apical system is usually about half the horizontal diameter, 

 though rather variable in size, from 43 to 53 per cent of the horizon- 

 tal diameter; it is usually somewhat elevated toward the middle. 

 The oculars are usually insert, sometimes very narrowly so, sometimes 

 more broadly; they are usually rather broad, more or less deeply exca- 

 vated in the outer edge, the inner edges being more or less S-shaped. 

 The genital plates are usually much narrower in their outer than in 

 their inner part. The genital pores are small, rather distant from the 

 outer edge. The periproct is of medium size, with a moderate number 

 of plates. The whole apical system is rather densely covered with 

 small tubercles of uniform size, only those at the inner edge of the 

 genitals and on the periproctal plates being sometimes comma-shaped 

 (fig. 19). 



The peristome is usually somewhat smaller than the apical system, 

 rarely a little larger, and quite flat. There are 10 or 11 ambulacral 

 plates in a series, and 5 or 6 interradial plates in a fairly regular 

 series; usually the ambulacra do riot join at the peristomial edge, 

 but the interradial plates do not reach to the mouth edge, even 

 where the way is left open for them. 



The primary spines are more or less slender, about one and one- 

 half to two times the horizontal diameter, or even a little longer; 

 they taper gradually to a simple blunt point. There are usually 9 

 or 10 sharp, rather coarsely serrate ridges, the surface being other- 

 wise not very densely covered by short, very fine, not anastomosing 

 hairs, which do not conceal the normal fine longitudinal striation. 

 The collar is short, thickening toward the not very conspicuous 

 milled ring. The oral primaries are very slender, straight, smooth, 

 or very finely serrated longitudinally. The third or fourth is tran- 

 sitional to the ambital spines. 



The secondary spines are slender and flattened; the scrobicular 

 spines are about 4 mm. long, usually distinctly concave on the out- 

 side, sometimes with nearly straight edges, sometimes distinctly 

 broader in the basal part and narrowing toward the slightly rounded 

 point. The marginal ambulacral spines are much narrower and more 

 simply spiniform. The miliary spines are flattened and pointed. 

 The secondary spines are scarcely appressed. 



Large globiferous pedicellariae are very rarely observed; they were 

 detected only in one specimen (station 5517). They are of the typ- 

 ical form with no end tooth (pi. 80, fig. 4) and with a limb on the 

 stalk. Small globiferous pedicellariae of two different forms occur; 

 one (pi. 80, fig. 6) is the ordinary typical form of the usual structure, 



