HYDROIDS OF EASTERN CAXADA 



163 



Tetrapoma quadridentatum (Hincks). 



Trophosome. " Hydrothecae cylindrical, usually 

 slightly incurved on one side, the height about three 

 times as great as the breadth, with a quadridentate 

 margin and an operculum comi>osed of four pieces, 

 borne on ringed pedicels of variable lengths (3 to 7 

 rings) which rise at intervals from a creeping stem " 

 (Hincks). 



Gonosome. Unknown. 



No. 58. 



Tetrapoma quadridentatum 

 (after Hincks). 



Family HALECIDiE. 



. .Trophosome. Hydrotheca- reduced to saucer-shaped hydrophores which usually 

 pass without constriction into the large tubular pedicels; margin entire, often flar- 

 ing; reduplication common: hydranths with conical proboscis. 

 Gonosome. Gonophores producing fi.xed sporosacs. 



Genus TIamxium. 



Trophosome. As in the family. 



Gonosome. Gonangia often of different shape in the two sexes which are found 

 on different colonies. 



KEY TO SPECIES. 



a Stem simple. 



b Stem annulated or wavy throughout. 



c Gonangium laterally compressed, small, with regular margin. 



H. tenellum. 

 cc Gonangium very large with wavy or spiny margin. 

 hh Stem not annulated. 



d Colony minute, with no definite main stem. 

 dd Colony large, with main stem and branches. 

 aa Stem fascicled. 



e Branches not fascicled. 



/ Gonangium large, aperture lateral. 

 // Gonangium smaller, aperture terminal. 

 ee Stem and main branches fascicled. 

 g Gonangium spiny. 

 gg Gonangium smooth. 



h Gonangium aperture terminal. 

 hh Gonangium aperture lateral. 



H. minutum. 



FT. curvicaule. 

 H. sessile. 



H. articulosum. 

 H. gracile. 



H. muricatum 



H. halecinum. 

 H. heani. 



Halecium articulosum Clark. 



Trophosome. Stem coarse, fascicled; primary 

 branches scarce but long, hence colony has a loose 

 appearance; branches alternate, pinnate; internodes 

 short and getting shorter towards the ends of the 

 branches, where they may be as broad as long; hydro- 

 thecae sessile; margin not flaring. 



Gonosome. Female gonangia large, obovate, borne 

 in rows on the upper side of the branches; aperture 

 lateral bui near the distal end; male gonangia oblong. 



79550—114 



No. 59. 

 Halecium articulosum. 



