15 
1912-13.] Hydroids of British Antarctic Expedition, 1908. 
Localities. — Bay (east of Cape Royds), 7-8 fathoms, on Gampanularia 
lobata, and 7-20 fathoms, June 1908, on Polyzoon ; 10-20 fathoms, May 
1908, on Sertularella cumberlandica. Cape Royds, 10-25 fathoms, July 
1908; 30-60 fathoms, 15th August 1908; 30-80 fathoms, August 1908, on 
Sertularella cumberlandica. 
Distribution. — Halecium tenellum has been recognised in all the great 
oceans, although it is more abundant and more widely distributed in the 
Atlantic and Arctic areas. In the Antarctic region fresh records are gradually 
exhibiting a general distribution: 70° 48' S. lat., 91° 54' W. long.; 70° 00' 
S. lat., 80° 48' W. long, (west of Alexander Land), Hartlaub, 1904; Booth- 
Wandel Island, Billard, 1906 ; M c Murdo “ Bay ” and neighbourhood, Hickson 
and Gravely, 1907 ; Gauss Station and Gauss-Berg, Vanhoffen, 1909; and 
the present records. 
Ophiodes arboreus (Allman). 
Halecium robustum , Allman, 1888, pi. iv. figs. 1-3; but not Halecium robustum , 
Alim., Ritchie, 1907, p. 524; nor Vanhoffen, 1910, p. 319, fig. 35. 
Halecium arhoreum , Allman, 1888, p. 10. Idem, Hickson and Gravely, 1907, p. 27, 
pi. iv. figs. 17-29 ; but probably not H. arhoreum , Alim., Jaderholm, 1905, 
p. 11, Taf. v. fig. 4. 
Ophiodes arboreus , Billard, 1910, p. 4. 
Many fragments which agree with Hickson and Gravely s description 
of this robust species occur in the collections from various localities. Un- 
fortunately, the fragments of the trophosome are in so bare a condition 
that only with the greatest difficulty could any trace of hydrothecse be 
discovered. These, however, enable me to represent them somewhat less 
diagrammatically than the authors of the Discovery report have done. 
This is the more important since the hydrothecse in the Antarctic specimens 
differ in detail from those of Allman’s type, as both Vanhoffen and Billard 
have remarked. The difference, however, as regards the length of the 
hydrothecse and their supports, is usually less marked than the figures in 
the Discovery report would indicate ; although, on the other hand, I 
cannot agree altogether with the remark (p. 28), contradicted by the figures, 
that the hydrotheca is “ adnate throughout its whole length.” As a matter 
of fact, there is some variation in the condition exhibited by the hydrothecse. 
While in the majority of cases a hydro theca is closely apposed to the inter- 
node, at least the margin is free, although it does not, or scarcely does, reach 
beyond the node. Sometimes, however, a hydrotheca occurs, generally 
towards the base of a hydroclade, which is not only quite free, but which, 
by the prolongation of the tubular portion which it caps, has been carried 
some distance beyond the node. These remarks refer to primary hydro- 
