. The Danish Ingolf-Expedition. Scientific expeditions; Arctic Ocean. ECHINOIDEA. II. en St. ii (64 34' 310 12'Long. W. [300 fathoms r°6 C. Bottom temp.) 2 specimens. 7(1(60° 50' 26° 50' 806 1 1 — )2 — 81 (6i°44' 27°c»' 485 6° 1 )2 (young) -83 (62° 25' - 28° 30' 912 3°5 - )3 One young specimen was further taken by the Tlior 1904 at 61 15'Lat N., 9° 35'Long. W. 900 Meter. This species is evidently nearly related to the Califoruian species Plexechinus cinctus A. Ag. It is, however, easily distinguished from the latter species by the very different outline of the pos- terior end of the test
. The Danish Ingolf-Expedition. Scientific expeditions; Arctic Ocean. ECHINOIDEA. II. en St. ii (64 34' 310 12'Long. W. [300 fathoms r°6 C. Bottom temp.) 2 specimens. 7(1(60° 50' 26° 50' 806 1 1 — )2 — 81 (6i°44' 27°c»' 485 6° 1 )2 (young) -83 (62° 25' - 28° 30' 912 3°5 - )3 One young specimen was further taken by the Tlior 1904 at 61 15'Lat N., 9° 35'Long. W. 900 Meter. This species is evidently nearly related to the Califoruian species Plexechinus cinctus A. Ag. It is, however, easily distinguished from the latter species by the very different outline of the pos- terior end of the test, the actinal keel being much higher and the anal snout much less prominent in the Atlantic than in the Californian species; the periproct is also more sunken in hirsutus. If it proves to be a constant feature in P. ductus that only three pairs of plates are in contact with the periproct whereas in hirsutus four pairs are so, this will be a very good distinguishing character. (In the PL Nordenskjoldi, to be described in the Report on the Echinoidea of the Swedish South Polar Expedi- tion, only three pairs of plates are in contact with the periproct). — The pedicellarise can scarcely be supposed to show more important differences. The genus Plexechinus is placed among the Pourtalesise by Agassiz, mainly on account of its anal snout and the position of the periproct; probably also other features: the elongated shape, the apical system, the disjointed sternum and the rudimentary phyllodes are taken as arguments in favour of such a position of the genus though it is not stated clearly. The genus certainly shows some Pourtalesian affinities, but it is evidently more nearly related to the Urechinidce. It differs essen- tially from the Pourtalesise and agrees with the Urechinids in having a flat peristome, one of the most prominent characters of the Pourtalesise being the vertical peristome at the inner end of a deep groove. Another feature of eminent importance is th
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