8 BULLETIN 74, UNITED STATES NATIONAL MUSEUM. 



appeared, and likewise some few of the plates at the actinal end of the area carry 

 only the ])riin!iry tul)orc'Ie. This holds good for the larger and the smaller of the 

 three specimens in hand; in the specimen of 27 mm. horizontal tliameter the small 

 inner tubercle has appeared on some of the plates near the apex and the peristome, 

 but quite irregularly. The pores are separated by a rather broad wall, which is 

 not at all elevatetl (Plate 16, fig. 12); the whole pore area is unusually flat and 

 even, not distinctly sunken. 



The interainbuliicra have a comparatively broad naked median line, which is 

 slightly sunken; this is also the case with the upper horizontal sutures. The areoles 

 are unusually low; only the two lowermost may be confluent (in larger specimens 

 probably more may be so). The upper tubercles are very distinctly crenulated, but 

 only on the abactiiial side. (Plate 14, fig.S.) The tubercles arounil the areoles are 

 distinctly larger than those outside; these latter are few in number and onl}' indis- 

 tinctly arranged in horizontal series on the median part of the ]ilate. 



The apical .system is 4S-o4 per cent of the horizontal diameter of the test; the 

 genital plates are almost rectangular, onlj' slightly broader within than without; 

 the outer edge is very little prominent; the ocular plates are rather large, heart- 

 shaped, more or less broadh* in contact with the anal plate. (Plate 15, fig. 12.) 

 In the smallest of the three specimens at hand they are all excluded from the anal 

 area. (Plate 7, fig. 6.) The periproct is covered with rather numerous small 

 plates. The whole apical system is somewhat sparsely covered with tubercles; 

 those on the ocular plates are generally rather characteristically arranged, forming 

 an arched series along the outer edge, just inside the ocular pore; those over the 

 pore are considerably smaller than those laterally ])Iaced. 



The peristome is from 42.. 5 to 45.5 percent of the horizontal diameter, in the 

 youngest specimen even 57 per cent; the interambulacral peristomial plates are 

 quite regular; they do not reach quite to the mouth edge, but the adjoining ambu- 

 lacral series do not, however, fully join at the inner edge. There are 1 1 ambulacral 

 plates in each series in the specimen of 27 mm. The pores of each pair are placed 

 nearly vertically (namely, one outside the other); the first pair is distinctly larger 

 than the following. 



The radioles are well shown in Plates 2-3; and the figures 18-27, Plate 2 of the 

 Blake Echini likewi.se represent them very well. They are very characteristic, dis- 

 tinctly striate, coarsely spinous in the proximal part, the spinelets diminishing and 

 disappearing toward the point. It is a very peculiar feature that these spines are 

 developed exclusively on the upper side of the radioles, the lower side remaining 

 almost entirely smooth, the longitudinal stride being here only finely serrate (com- 

 pare Plates 2-3). They aie somewhat tai)ering, and the jjoint may be somewhat 

 widened. This form of radiole is evidently the typical form, but another form 

 may occur in which the spines are not thus developed; the upper side of the radiole 

 is then not more s[)inous than the lower side, the whole radiole being finelv serrate 

 along the longituilinal striaj. Such radioles are figured in Plate 2, figs. 20 and 23 

 of VaeBlalce Echini, and according to Agassiz both forms may occur in one and the 

 same specimen. I have not seen that myself. In the largest and the smallest of 

 the specimens at hand the ladioles are all of the typical Sj)inous form, except some 

 of the uppermost; but these are young radioles, not yet fully formed, without 



