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38 TH. MORTENSEN, (Schwed. Südpolar-Exp. 



As pointed out by DöDERI.EIN 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 DODEKLEIN, 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 i, 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 2.5 — 3 mm. diameter. 

 This late appearance of the second tubefoot probably is the rule among the Echi- 

 nina [comp. e. g. Hypsiechinns coronatus (-Ingolf» Echinoidea I. p. 89), Sterechiims 

 Nejimayeri (Echinoidea d. deutschen Südpolar-Exped. p. 70)]. 



The primary spines are smooth, as stated by DÖDERLEIN; only in the young 

 specimens they are more or less thorny. De LorioL says that they are »nullement 

 arqués»; as I have stated in the »Ingolf» Echinoidea, and as also maintained by 

 DöDERI.EIN, they are really more or less distinctly curved near the actinostome, 

 though not so much so as in the Sterechhius species. The secondary spines are 

 often somewhat thickened in the point, not so very like those of Sterechinus Neu- 

 mayeri, as I have stated in the »Ingolfi Echinoidea I. p. 103. To DöDERLEIN's 

 description I may only add that there is no central thorn in the point; only the 

 point of the spine is thorny (PI. XVI Fig. 6). — I have been unable to find em- 



Fig. 12. .Apical system of Nctcchinits magel- 



lanicus. with abnormal development of the 



madreporic pores. Vi. 



