6 SVEN LOVEN, ECHINOLOdlCA. 



pentagonal space, covered by the general integument. In aii- 

 other specimen, fig. 5, this spaee has just beeii filled witli the 

 dorso-central disk, /<(/. 6, a still delicate pentagonal lamina of 

 reticulatcd caleified tissne, with its thin margins now over- 

 lying, now nnderlying tliose of the costals, in its niiddle thic- 

 kened and raised into the beginnings of a verrnca. In the 

 specimen. Pl. /, /?y. 2, the most advanced, the sntures are di- 

 stinctly seen throngh the covering, and the dorso-central disk 

 is well defined. The five provisional suckers are here strongly 

 contracted, seeniingly preparing to disappear, as observed long 

 ago by the late Augustus Kroiin. ^ All över the corona a 

 small number of secondar^' spines are present, but, what is 

 remarkable, there are only tvvo on every interradial plate, 

 and in this specimen as well as in the others there is no trace 

 of the eircles of flattened secondaries, whieh in the adult sur- 

 round the bases of the primary spines. This is also clearly 

 seen in another specimen of the same age 1,4 ra mm. in diame- 

 ter, carefuUy dried and denuded, Pl. II fuj. 7, 'S, .9. The dorso- 

 central disk of the calycinal system is distinct and, like the 

 five costals, presents a single verruca, while the large and 

 convex costal, that gives passage to the water-pore, bears 

 three to four. The radials, whicli appear to be somewhat 

 shortened and are provided each with a verruca, have the aper- 

 ture at the base of the sucker closed on its under side, fig. S. 

 At this age the ambulaera enter into the composition of 

 the coronal system with five pairs of plates, fig. 8, f>. The 

 innermost of these. the tive primordial pairs, are large, some- 

 what wedge-shaped, closely contiguous to one another, and 

 constitute by themselves alone the fii'st circle. A solution of 

 continuity is clearly seen to intervene between them and the 

 following pairs. These, the second to the fifth, form, as a 

 whole, the ambulacral constituents of the corona, fig. 8. They 

 are smaller, distincth^ hexagonal, and nearly twice as high as 

 they are broad. All the plates of the ambulaera are pier- 

 ced each with a pedicellar pore, and in all respects disposed 

 according to the law of heterotropy- maintained in the whole 



' MtJLL. Arch. l<S5i. p. .'551. It is also worth reniembering that, ten 

 years before, this arute ol)server had seen the ambnlaeral nervi; pass throu;rh 

 the pore into the pedicel, and there up to the sucking-disk. Mull. Aroliiv, 

 1811, p. 6. 



= Etudes s. 1. Echinoidées. p. 13 — K», Pl. ITT— IX. XTV. XVIT— XX, 

 XXII— LII. — Pourtalesia p. (!. 34. 



