2 TH. MORTENSEN, (Schwed. Siidpolar-Exp. 



The species represented in the collection of the South Polar Expedition are the 

 following, those marked with an * being also represented in the collection of the 

 Fuegian Expedition: 



Ctenocidaris speciosa n. g. n. sp. (South Georgia, Shag Rocks Bank, Graham Region). 

 * Austrocidaris canaliculata (A. Ag.) (Falkland Isl.). 



— spinulosa n. sp. » » 



* Arbacia Dufresnii (Blv.) (Coast of North Argentina). 



* Notechinus magellanicus (Phil.) (Coast of North Argentina, Tierra del Fuego, Falk- 

 land Isl., Graham Region). 

 Ster echinus Neumayeri (MEISSN.) (South Georgia, Graham Region). 



— Agassizii nom. nov. (for ^margaritaceusi) (Falkland Isl., South Georgia, 

 Shag Rocks Bank, Burdwood Bank). 

 * Loxechinus alius (Mol.) (Tierra del Fuego). 

 Plexechinus Nordenskj'dldi MRTSN (Shag Rocks Bank). 



Abatus ^'cavernosus (PHIL.), with the variety bidens, n. var. (South Georgia). 

 — Agassizii (Pfeffer) (South Georgia). 

 * Schizaster {Tripylaster) Philippii (Gray) (Coast of North Argentina). 

 Amphipneustes Lorioli KOEHLER (Graham Region). 



— Koehleri Mrtsn (South Georgia, Shag Rocks Bank). 



The collection thus contains in all 14 species, 4 of which are new, viz. Cteno- 

 cidaris speciosa, Austrocidaris spinulosa, Plexechinus Nordenskj'dldi and Amphi- 

 pneustes Koehleri; of the two latter there has already been published a preliminary 

 description. * The first of them also represents a new generic type. A new variety, 

 bidens, had to be established for a form of Abatus cavernosus. The study of Arba- 

 • cia Dufresnii revealed the fact that a quite different species has hitherto been con- 

 founded with it; this species is described here under the name of Arbacia crassispina 

 n. sp. 



Among the more interesting points mentioned in the present work I may name 

 the discovery, that Amphipneustes Koehleri shelters its brood, quite similar to 

 what is known in Abatus cavernosus; the description of the development of Abatus 

 cavernosus, from the formation of the apical plates until it has reached maturity, 

 the discovery of a distinct genital plate 5 being of special importance; further the 

 discovery of the remarkable Phyto-Parasite, Echinophyces mirabilis, described from 

 Rhynchocidaris triplopora MRTSN in the »Echinoiden der deutschen Stidpolar- 

 Expeditiom, in Ctenocidaris speciosa, where it produces analogous effects, the genital 

 openings being transferred to the middle of the corresponding interambulacra. 



* Th. Mortensen. Some new species of Echinoidea. Vid. Medd. Naturh. Foren. Kobenhavn 1905. 



