346 ERNEST WARREN. 



The liydrotlieca is provided with an internal ridge {rd.) 

 situated at about one third of the lieight of the hydrotheca 

 from the base. Along this ridge the hydranth is attached to 

 the sheet of ectodei-m lining the hydrotheca. 



The endoderni of the hydranth can be everted through the 

 mouth (fig. 38, e.e.) for a considerable distance, thus recalling 

 the condition seen in Eudendrium an gu stum. 



Systematic Position. — The present hydroid is allied to 

 Thyroscyphus simplex Allman,^ from Somerset, Cape 

 York, Torres Strait, in 8-12 fathoms of water, T. ramosus 

 Allman^ from Bahia, and Campanularia tor esii Bnsh^ 

 from Torres Strait. These three species exhibit a certain 

 bilat-eral symmetry in that the hydrotheca is distinctly more 

 ventricose on the adcauline than on the abcauline surface. In 

 T. asqualis, as the specific name is intended to imply, the 

 two surfaces are practically equal and symmetrical. Also 

 the stem is much more zig-zag than in the other species. 



In the present species, however, a bilateral symmetry is 

 still evident by the excentric position of the opening of the 

 diaphragm, it being situated nearer the abcauline side. From 

 this it would seem probable, either that tequalis is reverting 

 to a typical radial symmetry, or that it represents a stage in 

 the development of the bilateral sj^mmetry. 



II. 



Geographical Distribution of the Species. 



There have now been described 35 species; 15 of these 

 appear to be new, including two new genera. 



Of the 35 species 32 were found on the Natal Coast and 4 

 were dredged off Algoa Bay, one occurring in both localities. 



In the accompanying table the distribution of the species 

 is shown as far as can be traced with the available literature. 

 This list, notwithstanding its extreme incompleteness, exhibits 

 certain points of interest and significance. 



' AUman, G. J., ' Challenger Reports ' " Zool.." V. 



2 Bale. W. M.. ' Cat. of the Australian Hydroid Zoophytes.' 1884. p. 52. 



