Bd. VI: 4) THE ECHIXOIDEA. 5 



near the peristome and near the apical system in larger specimens. — The pores 

 are rather large, very close together, separated only by a very thin wall, which is 

 even generally interrupted in the middle, the pores thus becoming confluent (Fig. i). 

 The poriferous part of the ambulacral plates scarcely so broad as the non-poriferous 

 part; it is not so distinctly sunken. — 9 — 10 ambulacral plates correspond to each 

 interambulacral plate at the upper part of the test. 



Interambulacra. The aréoles are rather deep, all confluent except the three upper 

 ones, which latter alone are round, all the lower ones being oval. The median space 

 rather broad, closely covered by uniformly sized secondary tubercles, with numerous 

 small miliary tubercles between them. There is thus no naked space along the 

 scarcely depressed, median line. The beginning (at the median line) of the hori- 

 zontal sutures is generally marked by a more or less distinct depression. The tu- 

 bercles around the aréoles are not larger than the 

 other secondary tubercles. Also the rather narrow 

 margin outside the aréoles is closely covered by -^■^^ * 



secondary tubercles. w^^m' -^^^^ 



The apical system is somewhat less than half ' 



the horizontal diameter, ca. 40 — 47 %] in the quite 

 young specimens it is comparatively a little larger, 

 as seen by the measurements given above. The 

 ocular plates are all excluded from the anal system; 



they are rather deeply notched in the outer edge. Fig. i. .\mbulacral pores of Ctenocidaris 

 which is otherwise sometimes more angular, some- spicwsa. 



times more rounded (PI. IV Fig. 2, PI. XIII Fig. 2). The pore is surrounded by 

 a distinct elevation, like a ring-wall. They are covered by rather numerous small 

 tubercles, except a more or less broad margin along the inner and outer edges, which 

 remains bare. The genital plates are considerably broader than long, like the oculars 

 covered by secondary tubercles leaving the margin bare. The female genital openings 

 are very large, ca. 2 mm in diameter, close to the outer edge or even breaking 

 through the edge of the plate (Plate XIII Fig. 2). The male genital openings are 

 very small and remote from the edge (PI. IV Fig. 2). The anal area is covered by 

 an outer circle of rather large plates, inside which comes another circle of smaller 

 plates; the middle part is covered by quite small plates, which become more or less 

 elongate towards the anal opening. The whole anal system is, in the larger speci- 

 mens, generally much elevated; the elevation begins already outside the anal system, 

 the genital plates being more or less raised in their inner part. 



The peristome is somewhat smaller than the apical system, ca. 35 — 42 "o of the 

 h. d., but likewise comparatively a little larger in young specimens. The ambulacral 

 plates of the peristome are numerous, ca. 12 in larger .specimens; towards the outer 



