148 ECHINOIDEA. II. 



as mflavescei/s, where it has been worked out so very accurately by L,oven; it is, however, to be uoticed 

 that the two left genital plates and the right posterior one are generally distinctly separated from 

 the left anterior (with the madreporite). The genital pores I have not found in specimens smaller than 

 14™ length (in flavescens Loveu has found them already at a size of icr5 mm .) — The labrum only 

 reaches a little over the middle of the 1. adjoining ambulacral plates in specimens up to ca. i^"™ 

 length. In a specimen of 2 mm length it reaches the 2. ambulacral plate 011 the right side, and from a 

 size of ca. 3 mm it reaches the 2. ambulacral plate on both sides as in the grown specimens. The regular 

 pentagonal form of the peristome begins to alter at a size of ca. 3 mm ; in specimens of 4 mm length the 

 labrum is rather prominent, reaching the edge of the mouth-opening. The definitive form of the peri- 

 stome is found in specimens of ca. io mm length. — The front ambulacrum is distinctly sunken already 

 in specimens of 2 — 3 mm length; in yet smaller specimens the outline of the front end is almost straight, 

 like what is seen in the figures 172 and 173 of Loven. The tube-feet of the anterior ambulacrum 

 appear very early, as found by Loven in flavescens, but they are in no way especially large in the 

 young specimens, which fact is not in accordance with the view of Agassiz that very large suckers 

 are an embryonic feature (comp. above p. 96 sub Aeropsis rostrata). The large spicules of the frontal 

 tubefeet are distinct already in specimens of 3""" length. The paired petals, as usual, are considerably 

 later in their development than the anterior ambulacrum. Single pores begin to appear in the poste- 

 rior series of the anterior petals at a size of ca. 2'5 mm ; at ca. 3 mm they begin to appear in the posterior 

 petals, both series, and a little later (at ca. 4 mm length) they begin to appear in the anterior series of 

 the anterior petals, the pores of the posterior series at the same time beginning to elongate trans- 

 versely. At a size of scarcely 5 mm I find the pores (6 — 7 in number) of the posterior series of the ante- 

 rior petals double, this condition of the pores evidently being reached through the formation of a trans- 

 verse ridge over the elongated single primary pore. At a size of ca. 5 - 5 mm the petals are fully formed, 

 only the number of the double pores being smaller than in the grown specimens, viz. in the anterior 

 petals 3 — 4 in the anterior, 7 — 8 in the posterior series, and in the posterior petals 6 in the anterior, 

 7 in the posterior series. 



The fascioles make their appearance very early. At a size of only 07 — cr8 mm the subanal fasc- 

 iole is distinct, consisting to begin with of only a single circle of clavulae. The spines within the 

 fasciole are comparatively long, as long as the test, pointing directly backwards, which gives to these 

 small specimens a characteristic appearance. The anal branches from the subanal fasciole appear at 

 a size of ca. 2"5 mm . The inner fasciole is later in its appearance than the subanal fasciole, not begin- 

 ning to form until the animal has reached a size of ca. i"5 mm . It likewise consists at first only of a 

 single circle of clavulse. — The development of the subanal area also affords some features of interest. 

 In quite small specimens only the 6th ambulacral plate of the series I. a. and V. b. reaches within the 

 fasciole; at a size of ca. 2 - 5 m,n the 7th plate begins to expand towards the fasciole and by and by it 

 reaches within. From a size of ca. 8 mm the 8th plate begins to expand in the same manner. Only at 

 a size of 14 — 15™™ does the first pair of pores appear within the fasciole; the second pair (in the 8th 

 plates) I have not found developed at a smaller size than i8 mm . 



Pedicellarise do not appear till rather late, at a size of ca. 2"™, the triphyllous being the first 

 to appear; they show the structure so characteristic for the species already from their first appearance. 



