1 6 TH. MORTENSEN, (Schwed. Südpolar-Exp. 



really vary to a considerable extent. As correctly described in the iRevis. of Echini» 

 they are comparatively slender, slightly tapering, somewhat swelling at the base; 

 they are closely set with small thorns, longitudinally arranged, uniting into longi- 

 tudinal ridges towards the point (PI. XIV Fig. i8). Between the thorns the ostra- 

 cum is covered by rather coarse, bushshaped, somewhat anastomosing »hairs» (Fig. 5) 

 — a conspicuous difference from E. mit rix (comp. Taf. XIII Fig. 7, Echinoidea d. 

 deutschen Südpolar-Exped.). — The actinal radicles (Pi. XIV Figs. 7 — 8, 11) are 

 very little specialized, only gradually .shorter and with the thorns more or less re- 

 duced, sometimes quite smooth; the}- are not distinctly flattened or curved. 



o°o 0=°° 



o o 

 Fig- 5- Transverse section of radiole of Aiislrocidaris canaliailata. 'Vi. 



The secondary spines are generally appressed; those round the radioles are the 

 longest, ca. 3 mm., the primary ambulacral spines are a little shorter; the miliary 

 spines are scarcely half the length of the primary ones. The spines on the apical 

 system are very short, only those surrounding the anal opening are somewhat longer. 

 The smaller spines are cylindrical, the larger ones, especially those round the radioles, 

 are distinctly flattened and rather broad, not pointed. They are very smooth. 



The pedicellariae are rather inconspicuous and not very numerous. The large 

 globiferous pedicellariae are typically of the form shown in PI. VIII Fig. 32 of the 

 slngolfa-Echinoidea I; but they may vary not inconsiderably. The side-edges do not 

 always proceed as far as the terminal opening, but may end at a shorter or longer 

 distance below; but they may also pass almost to the very point of the valve, the 

 opening thus lying within the blade, and in this case the opening may be somewhat 

 smaller than usual. On the other hand it must be noticed that a form recalling 

 that of the large globiferous pedicellariœ of Ajistrocidm-is Lorioli, figured in the 

 »Ingolf>-Ech. I. p. 170 Fig. 7. was never met with in any of the specimens examined 



