12 THE VOYAGE OF H.M.S. CHALLENGED. 



the exserted portion being of a very thin and delicate texture rarely shows the orifice 

 in a perfect condition. It may perhaps be identical with M. d'Orbigny's Idmonea 

 canwiensis (Palseont. Frang., p. 732) ; but as neither figure nor sufficient description of 

 that species are given, and it is merely stated to be " slender as a thread and almost 

 round, with very few cells," it is impossible to be certain. 



(4) Idmonea australis, Macgillivray (PL III. fig. 3). 



Idmonea australis, Macgilliv., loc. cit, Dec. vii. p. 30, pi. Ixviii. fig. 2. 

 , Character. — Zoarium of small size (| to f inch), irregularly branched once, each 

 short branch terminating in a single fork ; branches contorted and sometimes twisted ; 

 four to six zooecia in each series, the inner the longest ; no intermediate longitudinal 

 space in front between the series'. Zooecia very slender (0'12 mm.), connate below, but 

 when perfect much produced or free for one-half or two-thirds of their length, slightly 

 tapering, some nearly straight and ascending obliquely, but towards: the upper part of 

 the branches curved forwards, not flattened in front; series 0"7 to I'O mm. apart. 

 Branches compressed, rounded both in front and behind, about "6 mm. wide, everywhere 

 minutely dotted, up to the border of the aperture ; dorsal surface very finely striated 

 longitudinally, intermediate spaces with very minute dots in irregular longitudinal series. 



Habitat. — Station 163b, ofi' Port Jackson, 30 to 35 fathoms, rock. Ofi" Marion Island, 

 50 to 75 fathoms. 



[Port Phillip Heads, 10 to 15 fathoms, Macgilliv.] 



A very distinct and well-marked species, easily recognisable by the compressed form, 

 of the branches, which on section are oval, as well as by the extremely fine punctation, 

 6r rather white dotting of the surface, and the fine or close longitudinal striation of the 

 dorsal aspect. It appears to vary very much in the length of the exserted portion of the 

 zooecia, which, in the specimens from Marion Island, forms more than half the length of 

 the cell (PI. III. fig. 3). The exserted part is very slightly tapering and no part of it 

 appears to be peristomal, as the wall exhibits the minute punctation quite up to, :the 

 orifice, and there is very rarely any appearance of annular lines of growth. . None of the 

 specimens present any ocecial chamber. 



Mr. Macgillivray suggests that this species may prove to be a form of Idmonea 

 atlantica, but for this view I can see no grounds whatever. 



(5) Idmonea ehoracensis, n. sp. (PI. III. fig. 4). 



Character. — Zoarium very small, not more than ^ inch high; branches very short 

 and irregular, once furcate, much compressed, 0"6 mm. wide ; dorsal aspect rounded, longi- 

 tudinally striated but not grooved. Striae (fig. 4c), about 0"01 mm. apart, a single irregular 



