ON THE HYDROIDS OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 525 



frequently have at their bases at least one athecate internode connecting the stem 

 process with the hydrophore-bearing portions of the branch. The present specimens 

 are also frequently annulated, while Allman's figures indicate that the original was 

 smooth. 



Halecium tenellum, Hinks, 1861. (PL II. fig. 4.) 



Several specimens of an extremely delicate and graceful hydroid colony, growing 

 in bunches on the exposed axis of an Alcyonarian, are referable to this species. As 

 Hinks's description appears to be rather vague, I give a detailed description of the 

 specimens. The colonies are short, generally about 15 mm. in length, with un- 

 fascicled stems and irregular branches, which arise from the distal ends of the inter- 

 nodes, and in some cases, at least, from the base of a hydrophore. The branches lie for 

 the most part in one plane. 



The stem is thin, having near its base a diameter of a little over O'l mm., and, 

 like the branches, it is divided into long slender internodes whose length varies between 

 0*8 and 0*9 mm. The internodes are separated by slanting nodes, between which 

 the stem zigzags, and on each side of which are annular constrictions. The hydrothecse, 

 which are alternate and lie in one plane, are borne on short processes at the distal 

 ends of the internodes. They are cylindrical, trumpet-shaped, with a large, beautifully 

 everted limbus, and are usually prolonged by several similar segments (from two to 

 five in number), at the bases of which, on a level with the margin of the next lower 

 limbus, arise well-marked annulations. The diameter of a limbus from margin to 

 margin is 0"15 mm. 



The fleshy parts are in good condition, and the following points were observed : — 

 The hydranths are large and not wholly retractile, measuring, from mouth of hydrotheca 

 to summit of hypostome, when extended, 0*3 mm. Just above the neck there is 

 a well-defined bulge, and above this again a disc, from the margin of which arise the 

 tentacles, about sixteen in number, enclosing the conical hypostome. Across the in- 

 terior of the hydrotheca, at the level of the base of the everted limbus, stretches a 

 flattened fleshy disc supported by a perisarcal septum through which, by a small 

 aperture, the coenosarc passes. The disc is moored in its place by numerous delicate 

 strands attached to the perisarc at rather irregular intervals. At the points of attach- 

 ment there arise from the limbus small, dome-shaped prominences, which, refracting the 

 light, appear as minute, clear dots — the " refringent puncta " of the Challenger Report. 

 The prominences are rather irregularly arranged just above the level of the septum, 

 on which the coenosarcal disc lies, and vary in number from about sixteen to twenty on 

 each limbus. 



Gonosome. — The gonangia are ovate, broad in the proximal region, obtusely pointed 

 in the distal. They are supported on short stalks which arise from the sides of the 

 hydrothecse, and always from the lowest segment in any hydrotheca-tier. They are 

 9 mm. in length by 0'45 mm. in maximum diameter. 



