36 
TH. MORTENSEN, 
(Schwed. Südpolar-Exp. 
that it had been better to reexamine the question, than to suggest that I would 
be so foolish as to place Tetrapygus in another family than the Arbaciidae. Cer- 
tainly the figure given by DUNCAN & Sladen does not look very convincing. 
— I have carefully examined the ambulacral structure of Tetrapygus niger 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. Dufresnii (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 augmentation 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 (Phil.). 
PI. XVI Figs. 3, 6, 9 — 12, 19. 
? Echinus margaritaceus Lamarck. 1816. Animaux sans vertèbres. III. p. 47. 
? — — • 1846. Voyage de la Frégate Vénus. PI. VI. Fig. I. 
— ??iagellanicus Philippi. 1857. Vier neue Echinodermen des chilenischen Meeres. Arch. f. Natur- 
gesch. p. 130. 
— — A. Agassiz. 1872 — 74. Revision of Echini p. 123, 492. 
— — i 874 - Echinoidea of the Hassler-Expedition p. II. PI. III. Fig. 5 
— margaritaceus. — — — — — — p. 11. PI. III. Fig. 4. 
— magellanicus. F. Jeffr. Bell. 1881. Echinodermata of the »Alert». Proc. Zoöl. Soc. p. 90 — 91. 
— — M. Meissner. 1900. Hamburger Magalh. Sammelreise p. 10. 
— — R. Koehler. 1901. Échinides et Ophiures. »Belgica» p. 4. 
Slerechinus — Th. Mortensen. 1903. »Ingolf» Echinoidea. I. p. 103, 177. PI. XIX. Figs, 
il, 17, 23. 
Echinus — De Loriol. 1904. Notes pour servir à l’étude des Echinodermes. 2 Ser. Fasc. II. 
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, XLVII, Fig. '5. 
— , var. neu-amsterdami Död. 1908. Koehler, Stéllérides, Ophiures et Échinides. Expéd. 
antarct. nat. Écossaise. Trans. R. Soc. Edinb. XLVI. p. 616. 
Non: Echinus magellanicus. Ramsay. 1885. Cat. Echinod. Australian Museum. I. p. 21. 
— Farquhar. 1898. On the Echinoderm Fauna of New Zealand. Proc. Linn. 
Soc. N. S. Wales p. 320. 
— — Hutton. 1904. Index Faunæ Novæ Zelandiæ 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- 
