Bd. VI: 4 ) 
THE ECHINOIDEA. 
25 
of canaliculata is somewhat exaggerated, on account of the previous confusion with 
other species, I have shown above. That the length of the radioles may vary con- 
siderably in canaliculata I do not deny (though I should like to examine for myself 
some specimens of the longspined variety); but — so far as I know — no specimens 
have been described resembling A. spinulosa in the coarsely thorned upper radioles. 
This feature alone gives this species a very characteristic appearance, so that it is 
easily distinguished at the first glance. Also the smaller number of coronal plates 
and the not sunken abactinal area appear to me quite good specific characters, 
whereas the differences shown by the pedicellariæ are rather too inconspicuous to 
be of much value. — It may be possible, of course, that a larger series of speci- 
mens will reveal such as are intermediate between spinulosa and canaliculata. For 
the present, however, such intermediate forms are not known, and judging from the 
material at hand it is necessary to maintain spinulosa as a distinct species. 
The fossil Goniocidaris jorgensis described by De Loriol (Notes pour servir 
à l’étude des Échinodermes. II. Ser. Fase. I. 1902. p. 8) evidently also belongs to 
the genus Austrocidaris. The few isolated interambulacral plates — all that has been 
found of the species — show the inner edge smooth and depressed, »indiquant l’ex- 
istence d’un sillon le long de la suture médiane des aires interambulacraires, identique 
à celui que l’on remarque dans le Goniocidaris canaliculata Al. AgaSSIZ, par ex- 
emple». As the fossil species proceeds from the Lower Patagonian, probably be- 
longing to the Eocene, we may herein see evidence that the genus Austrocidaris 
has originated in the same region, where it still lives (and the only region, where 
it occurs) — and it would seem not unreasonable to suppose that the Austrocidaris 
jorgensis is the ancestor of the recent species of the genus. 
It may not appear very improbable to suggest that the Cidaris julianensis de- 
scribed by De LORIOL from the same formation (Op. cit. PI. I. Fig. 13) might be 
nearly related to the recent Ctenocidaris speciosa. The interambulacra are evidently 
very similar in structure, and the ambulacral pores, according to the figure given by 
De Loriol, are likewise separated only by a narrow wall. — This case is, however, 
not so evident as Austroc. jorgensis. 
Fam. Arbaciidae. * 
Arbacia Dufresnii (BLV.). 
PI. V Figs. 4 — 12. PI. XV Figs. 2 — 3, 6, S — 10, 13. 
Echinus Ditfresnii Blainville. 1825. Dictionnaire d. sciences nat. Vol. 37 . p. 75. 
— — — 1834. Manuel d’Actinologie. p. 226 
* The mode of writing » Arbaciadae», used by Agassiz & Clark is grammatically incorrect, in the 
same manner as sEchinometradae» for Echinometridae. It does not appear why they do not write also 
»Saleniadæ» etc. 
4 — 100133. Schwedische Südpolar- Expedition içoi — rçoj. 
