Echinoidea of the Swedish South Polar Expedition echinoideaofswed00mort Year: 1910 38 TH. MORTENSEN, (Schwed. Siidpolar-Exp. As pointed out by DODERLEIN it is the ocular plate opposite the anal opening (ocular I) which is in contact with the periproct; there is, however, some variation in this respect. In the larger specimens it seems to be a general case that two ocular plates are in contact with the anal area, viz. I and II or I and V, or even II and V; the latter case is found also in the specimen figured by DODERLEIN, PI. XXVII Fig. 9. Seldom all the ocular plates are excluded from the p
Echinoidea of the Swedish South Polar Expedition echinoideaofswed00mort Year: 1910 38 TH. MORTENSEN, (Schwed. Siidpolar-Exp. As pointed out by DODERLEIN it is the ocular plate opposite the anal opening (ocular I) which is in contact with the periproct; there is, however, some variation in this respect. In the larger specimens it seems to be a general case that two ocular plates are in contact with the anal area, viz. I and II or I and V, or even II and V; the latter case is found also in the specimen figured by DODERLEIN, PI. XXVII Fig. 9. Seldom all the ocular plates are excluded from the periproct, except in the quite young specimens. In a specimen of 4 mm. diameter the ocular plate I is still excluded but reaches very near to the edge. At this size the genital pores have not yet appeared, and the anal plate covers almost the whole anal area, only a pair of small plates having just appeared at its anal edge. At a size of scarcely 5 mm. diameter the genital pores have appeared. — In one of the largest specimens there are in the genital plates 1, 3 and 4 some small pores near the genital pore, which quite look like supplementary madreporic pores; but as the specimen had been dried, before I remarked these small pores, I dare not affirm that they are really madreporic pores. In another specimen, however (40 mm. in diameter, stat. 44), I find a small group of undoubted madre- poric pores in the two plates adjoining the madreporite, Ocular III and Genital 3, so here we have an extension of the madreporite (Fig. 12). In the young specimens the buccal plates show the feature that only one tubefoot is developed in each pair; the second tubefoot appears at a size of —3 mm. diameter. This late appearance of the second tubefoot probably is the rule among the Echi- nina [comp. e. g. Hypsiechinus coronatus (»Ingolf» Echinoidea I. p. 89), Sterechinus Neumayeri (Echinoidea d. deutschen Sudpolar-Exped. p. 70)]. The primary spines are smooth, as stated by DODERLEIN; onl
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