Bd. VI: 4) THE ECHINOIDEA. 9 



one on each ambulacral plate. There are 7 — 8 ambulacral plates on the peristome 

 and 2—3 interambulacral plates, which do not reach the mouth-edge. The genital 

 openings have just appeared. Otherwise the specimen agrees with the adult speci- 

 mens in all essential features, only the test is still much flatter than in the adult, 

 as appears distinctly from the measurements given above. 



One specimen from Stat. 17 and another from Stat. 22 differ in several respects 

 rather considerably from the typical specimens, so that I have been much in doubt, 

 whether they really belong to this species. I think, however, the conclusion to which 

 I have finally arrived is correct, viz. that they are specimens of Ctenocidaris speciosa 

 infested with the curious parasitic organism, Echinophyces mirabilis (comp. Echinoiden 

 d. deutschen Sudpolar-Expedition p. 12 — 17) and abnormally developed on account 

 thereof, analogous to the abnormal development of Rhynchocidaris triplopora when 

 infested with this parasite in its radioles. But, on account of the scarce material at 

 hand, it can scarcely be regarded as fully beyond doubt that this conclusion is the 

 right one. 



The measurements of the two specimens are as follows: 





Diameter. 



Height. 



Apical syst. 



Anal syst. 



Peristome. 



Number of 

 ambulacral 

 plates. 



Interamb. 

 plates. 



Radioles. 



St. 17 



23 mm. 

 23-S " 



.1 

 •I 



IO 

 12 



6-7 



6-7 



12 



12 



3 2 - 33 



33- 34 



6-7 



30 mm. 



20 » 



In the general structure of the test they do not differ from Ctenocidaris speciosa; 

 the fact that the ambulacral plates have, with a few exceptions, only one secondary 

 tubercle inside the primary one certainly depends on age. More noteworthy is the 

 fact that in the specimen from St. 17 Ocular III is in broad contact with the anal 

 plates and Ocular V nearly so; in the other specimen all the ocular plates are ex- 

 cluded. The peristome has, in the specimen from St. 17, only a few small interamb- 

 ulacral plates near the edge, in the other specimen none at all, the ambulacral plates 

 being unusually broad and uniting with those of the neighbouring series throughout 

 the whole length of the series, a conspicuous difference from the normal specimen of 

 18.5 mm. in which the interambulacral peristomial plates are already very distinct. 

 The structure of the radioles is conspicuously different from those of the typical 

 specimens; the ostracum is covered with the usual anastomosing »hairs», but these 

 end in numerous very fine points, not in single, comparatively coarse thorns as in 

 the normal specimens (PI. XIII Fig. 5 comp. with the Fig. 3 here given). Further 

 the actinal radioles have not the coarse dentations as in the typical specimens. 



2 — 100133 Sckwedische Sudpolar-Expedition igoi — igoj. 



