10 SVEN LOVEN, ON A RECENT FORM OF THE ECHINOCONID^. 



interiör into ten compartments, are here, in the close vicinity 

 of the peristome, only indicatecl by the convexity of each 

 series of interradial plates. By means of the arrangement thus 

 described the peristome becomes internally surroiinded by a 

 slio^htly funnel-shaped ring composed of five broad pieces for- 

 med by the interradially connected auricles, and leaving room 

 between them for the compressed middle parts of the ambulacra 

 with their approximated zones of pedicellar pores. It will 

 seem as if a somewhat similar disposition maintains also in 

 the Galerites Albogalerus. But it is not with this strueture 

 that our recent form accords in tlie corresponding parts; by 

 its separate and vmconnected lougitudinal auricles it decidedly 

 approaches the group formed by Pygaster, Pilens and Holec- 

 typus. 



Revertinof now to the outside, there is seen close to the 

 peristome the hollow of the single spherid with its minute 

 tiibercle. !Nothing like this is found in the Pygaster semi- 

 sulcatus of which the peristomal portion of the ambulacrum 

 V is given Pl. 2, jig. 11. Here the tubercles, primary and 

 secondary, evidently aiford no room for a hollow^ like that re- 

 presented PL 1, fig. 7. It is, however, so little probable that 

 this organ, of all but universal presence amoug the Echinoi- 

 dea, should be really absent in Pygaster, that it raay be al- 

 lowed to question whether in this genus the spherid, single 

 or double, was not entirely interiör, concealed in one or two 

 crypts excavated in the thickness of the test, as it is in cer- 

 tain Clypeastridae ^), for instance Clypeaster and Arachnoides, 

 in which the outward aspect in no wåse betrays its hidden 

 presence. 1 tried to find an answer to this question by care- 

 fully grinding down the test of a Pygaster semisulcatus, but 

 without success. In our recent Echinoconid the spherids are 

 single, as they are in Echinarachnius, Mellita, Laganum, Echi- 

 nocyamus, and it may be allowable to suggest that possibly 

 during life they were, as in those genera, in part or wholly 

 roofed över by a thin covering, which has disappeared in the 

 dead specimen. 



In the ambulacra of the Pygaster semisiilcatus the plates 

 following upon the three iirst coalescent ones are all simple 

 and cntire. At first a tendency shows itself towards forming 



') Etudeä s. 1. Echinoidées, p. 6, t. VIII, fig. 68—78. 



