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



that it had been better to reexamine the question, than to suggest that I would 

 be so fooHsh as to place Tctrapygus in another family than the Arbaciidœ. Cer- 

 tainly the figure given by DuNCAN & Sladen does not look very convincing. 

 — I have carefully examined the ambulacral structure of Tctrapygus nigcr and find 

 that Duncan and Sladen were wrong in their statement; it is not of the echinoid 

 type (PI. XV Figs. 12, 15). A comparison with the ambulacral plates of an Arba- 

 cia, e. g. A. Dufresiiii (PI. XV Fig. 3), leaves no doubt that the demi-plate imme- 

 diately below the large primary plate is the lower component of the compound plate. 

 Tetrapygus niger thus differs from the genus Arbacia in regard to the ambulacra 

 only in the augmen:ation of the demi-plates above the large primary plate — it is 

 of the diadematoid type, as might be supposed beforehand. My view of the im- 

 portance of the ambulacral structure in regular Echinoidea is not altered. 



Fam. Echinidae. 

 Notechinus magellanicus (PniL.). 



PI. XVI Fif^s. 3, 6, g— 12, ig. 



? Echinus margaritaceus LAMARCK. 1816. Animaux sans vertèbres. IIL p. 47. 

 ? — — 1846. Voyage de la Frégate Vénus. PI. VL Fig. i. 



— magcllanicns Phii.IPPI. 1857. Vier neue Echinodermen des chilenischen Meeres. Arch. f. Xatur- 



gesch. p. 130. 



— — K. Agassiz. 1872 — 74. Revision of Echini p. 123, 492. 



— — — 1S74. Echinoidea of the Hassler-Expedition p. II. I'l. III. Fig. 5 



— margaritaceus. — — — — — — p. II. I'l. III. Fig. 4. 



— magellanicus. F. Jeffr. Beli,. iSSl. Echinodennata of the >.\lertJ. Proc. Zool. Soc. p. 90 — 91. 



— — M. Meissner, igoo. Hamburger Magalh. Sammelreise p. 10. 



— — R. KoiiHLER. 1901. Echinides et Ophiures. »Belgica» p. 4. 



Sterechinus — Th. Mortensen. 1903. >Ingolfi' Echinoidea. I. p. 103, 177. PI. XLK. Figs. 



II, 17. 23. 

 Echinus — De Loriol. 1904. Notes pour servir à l'étude des Échinodermes. 2 Ser. Fasc. IL 



p. 13. PI. I. Figs. 7—9. 

 — — R. Koehler. 1906. Stéllérides, Ophiures et Échinides. Expédition antarctique 



Française (1903 — 1905) p. 30, 35. 

 Notechinus — L. Döderlein. 1906. Echinoiden d. deutschen Tiefsee-Expedition p. 227. Taf. 



XXVII, Fig. 9, XXVIII, Figs. 3—4, XXXV. Fig. 15, XLVIl, Fig. 5. 



— — , var. neu-amstirdami DöD. 1908. KoEHLER, Stéllérides, Ophiures et Échinides. Expéd. 



antarct. nat. Écossaise. Trans. R. Soc. Edinb. XLVI. p. 616. 

 Non: Echinus magellanicus. R.\MSAY. 1SS5. Cat. Echinod. Australian Museum. I. p. 21. 



— — Farquhar. 1898. On the Echinoderm Fauna of New Zealand. Proc. Linn. 



Soc. N. S. Wales p. 320. 



— — Button. 1904. Index Faunae Novœ Zelandiae p. 289. 



This very characteristic species has been so carefully described, especially by 

 De Loriol and Döderlein, that only very little additional information can be given. 

 Döderlein (Op. cit. p. 230) has given measurements of some specimens; as, how- 



