38 
TH. MORTENSEN, 
(Schwed. Südpolar-Exp. 
As pointed out by DöDERLEIN 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 DöDERLEIN, 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 2.5 — 3 mm. diameter. 
This late appearance of the second tubefoot probably is the rule among the Echi- 
nina [comp. e. g. Hypsiechinus coroncitus (»Ingolf» Echinoidea I. p. 89), Sterechinus 
Neumayeri (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 
DöDERLEIN, they are really more or less distinctly curved near the actinostome, 
though not so much so as in the Sterechinus 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 »Ingolf» 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 Notechimis magel- 
lanicus. with abnormal development of the 
madreporic pores. 5 /i. 
