ARBACIIDAE 215 



Family ARBACIIDAE 

 Arbacia Dufresnii (Blainville) 



Arbacia Diifresiiii, P. de Loriol, 1904. Notes pour servir a I'Etude des Echinodermes, 2 Ser., 



II, p. 8, pi. ii, figs. 2-5. 

 A. Dufresnii, Agassiz and H. L. Clark, 1908. Hawaiian Echini. The Salenidae, Arbaciadae, 



etc., p. 69, pi. 47, figs. i-ii. 

 A. Diifresv/i, Mortensen, 1910. Swedish South Polar Exped. Echinoidea, p. 25, pis. v, 



figs. 4-12; XV, figs. 2-3, 6, 8-10, 13. 

 A. Dufresnii, H. L. Clark, 1925. Cat. Recent Sea-Urchins Brit. Mus., p. 69. 

 A. Dufresnii, Mortensen, 1935. Monogr. Echinoidea. II, p. 579. 



St. 1321. 16. iii. 34. Cockburn Channel, Tierra del Fuego, 66 m. 4 specimens and 4 dead tests. 



St. WS71. 23. ii. 27. 6 miles N 60° E of Pembroke Light, East Falkland Islands, 80-82 m. 

 I specimen. 



St. WS 81. 19. iii. 27. 8 miles N 11° W of North Island, West Falkland Islands, 81-82 m. 

 3 specimens. 



St. WS 83. 24. iii. 27. 14 miles S 64° W of George Island, East Falkland Islands, 129-137 m. 

 8 specimens. 



St. WS 85. 25. iii. 27. 8 miles S 66° E of Lively Island, East Falkland Islands, 79 m. 2 specimens. 



St. WS 583. 2. V. 31. 53° 39' S, 70° 54' W, 14-78 m. I specimen. 



St. WS 755. 2i.ix. 31. 51° 39' S, 57° 39' W, 75 m. 2 specimens. 



H. L. Clark {pp. cit., 1925) has called attention to the remarkable fact that this species 

 has never been recorded from the Falkland Islands. Upon zoogeographical grounds it 

 was rather inexplicable that it should not occur there, the Falkland Islands being so 

 integral a part of the Magellanic region, where this species otherwise is widely distri- 

 buted. It extends up to the La Plata River on the east coast and to 42° S on the west 

 coast (Puerto Montt), and also as far south as the Antarctic Coast (Booth Wandel 

 Island, cf. below), its range in depth being from the littoral region down to ca. 300 m. 

 It is thus very satisfactory that the species has now been found to occur also off the 

 Falkland Islands. 



The species might well be expected to occur also ofT South Georgia ; but as it has 

 never been recorded from there, and as it is not represented in any of the numerous 

 dredgings off South Georgia by the ' Discovery ' it would seem to be a fact that it does 

 not occur there. This induces one to think that there must be something wrong with 

 the single specimen from the Antarctic coast (Booth Wandel Island) brought home by 

 the Expedition Charcot (cf. Koehler, 1906, Stellerides, Ophiures et Echinides. Exped. 

 Antarct. Fran9aise, 1903-1905, p. 29). As a misidentification is hardly thinkable, I cannot 

 help suggesting that there must be a mistake with the label, the specimen having in 

 reality been obtained from some South American locality. If the species really occurs 

 on the Antarctic coast, it is strange that the Discovery as well as all the other Antarctic 

 expeditions failed to find it to the south of South America. 



In view of Bernard's statement (Echinides recueillis par rExpedition du Cap Horn, 

 Bull. Mus. d'hist. nat. Paris, 1895) that this species is brood-protecting, rearing its 

 young on the buccal membrane, it is important to notice that there is no indication that 

 any of the specimens at hand carry the young ones on the peristome. Moreover, I think 



