. Echinoidea of the Swedish South Polar Expedition. Sea urchins. Bd. VI: 4) THE ECIIINOIDEA. 29 spicules in the upper part of the tubefeet; they are more or less irregular, with some perforations in the broader middle part (Fig. 7). This species was taken by the Expedition only at Station 2, the coast of North Argentina (370 50' Lat. S. 56°u' Long. W. 100 m.); 4 large, high specimens. From the Fuegian Expedition there are several large and small specimens from Bahia inutil, 1 —11 fathoms, 1896, Ultima Esperanza, 7—10 fathoms, stones, algae, ,3 specimens, Puerto Madryn, 5 fathoms, sand-clay bot
. Echinoidea of the Swedish South Polar Expedition. Sea urchins. Bd. VI: 4) THE ECIIINOIDEA. 29 spicules in the upper part of the tubefeet; they are more or less irregular, with some perforations in the broader middle part (Fig. 7). This species was taken by the Expedition only at Station 2, the coast of North Argentina (370 50' Lat. S. 56°u' Long. W. 100 m.); 4 large, high specimens. From the Fuegian Expedition there are several large and small specimens from Bahia inutil, 1 —11 fathoms, 1896, Ultima Esperanza, 7—10 fathoms, stones, algae, ,3 specimens, Puerto Madryn, 5 fathoms, sand-clay bottom, IO/XI 1895; 5 specimens. The question whether Arbacia alternans (TROSCHEL) is only a synonym of A. Dufresnii or represents a distinct species, has been very much discussed and a general agreement has not been reached as yet. LoVEN decidedly regards A. alternans as distinct, as does also StUDER. Likewise it is named as a separate species by Meissner in Bronn's »Classen u. Ordnungen d. Tierreichs», Echinoidea p. 1360. De LORIOL (Op. cit.) maintains that in the characters of the tuberculation of the abactinal side — the character upon which alternans is mainly established — no constant difference Ficr ? Spicules can be found, but he thinks the characters in the pedicellarias pointed from the tubefeet out bv STUDER »bien plus que l'arrangement des tubercules doivent of A'baLia ^"f1 lS engager a maintenir XA. alternans comme espece distincte». AGASSIZ (»Challenger» Echinoidea) evidently regards alternans as synonymous with Dufresnii since he does not mention the former in his list of the known species of recent Echini (p. 209). In the latest, very important, contribution to the knowledge of this group of Echinoids, viz. AGASSIZ & Clark's »Hawaiian and other Pacific Echini. The Arba- ciadae ; both alternans and afrieana TROSCHEL are regarded as synonyms of Dufresnii (p. 68), with the reservation that >;it is possible that further material from
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