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 Südpolar-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. 
II 
10 
6-7 
12 
32—33 
7 
30 mm. 
»22 
2 3 -S » 
I 1 
12 
6-7 
12 
33-34 
6-7 
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 Schwedische Südpolar-Expedition iqoi — igop. 
