A COLLECTIOX OF HYDKOIDS. 329 



there are also a certain nniiiber on the stem below the 

 proximal pinnas. 



Nematocysts from mesial nematophore 45 jli in lengthy and 

 6'2 ju in breadth. 



Diameter of main stem 0'50 mm., diameter of branch 

 0*263 mm., thickness of perisarc 34^, diameter in the region 

 of the pinmv 0'152 mm., diameter of pinna, front view, 

 0'071 nnn., side view, 0"121 mm. 



Hydrotheca. — Laterally compressed (fig. 34), viewed 

 from the side ventricose (fig. 33). Margin with a broad angular 

 lobe on each side, and a curved, s])ine-like tooth in front 

 {sjyi.). Intra-thecal ridge situated low down towards the base. 



Viewed from the side, height of hydrotheca 0'202 mm., 

 width 0*223 mm. Viewed from the front, diameter of mouth 

 0*182 mm., diameter at the middle 0*131 mm. 



Hydranth. — About 12-13 tentacles. 



Gonosome. — Not known. 



Histology. — The mesial nematophore in longitudinal 

 vertical section is shown in PI. XLVIII, fig*. 35. A well- 

 developed battery of nematocysts {B.n.) is present. At the 

 base there is an aperture in the perisarc (figs. 33 and 34, o.$.) 

 through Avhich a sarcostyle {s.), without a sarcotheca, pro- 

 trudes. At the base of this sarcostyle there can generally be 

 found a large cell {e.g.) filled with very large refringent 

 globules wliich have the general appearance of yolk. Similar 

 cells can also be found in the general tissue of the coenosarc. 



The hydroid is characterised by its dark colour. The 

 colour is due to the presence of cells containing numerous 

 small globules of dark refringent substance (figs. 35 and 36, 

 C.J).). These cells occur both in the ectoderm and endoderm 

 {ect.j e}id.). In the case of S. loculosa, in addition to the 

 black form, a colourless condition occurs. It is possilde that 

 such is also the case in H. segmentata. 



Systematic Position. — The present hydroid is undoubtedly 

 closely allied to Halicornaria mitrata Allman,^ of un- 

 ^ Allnian. G. J.. "* Description of Australian. Cape, and other 

 Hydroida." ' Linn. Soc. Journ. Zool.,' vol. xix, 1885, p. 1.53. 



