A COLLECTION OF HYDROIDS. 



317 



Diameter of stem, about at the middle and in tlie centre of 

 aninternode, 0"116 mm., thickness of perisarc 17//. Diameter 

 at the middle of a pinna 0'042 mm. 



Hydrotheca. — Cup-shaped, shallow, adnate by the whole 

 adcauline surface. 



Height 0-057 mm., breath O'lOl nnn. 



Hy dranth. — 18-20 tentacles. Nematocysts occur especially 

 at the tips of the tentacles, 2*3 fx in length, and 0'7 fx in 

 breadth. 



Text-fig. 13. 



Sxdo 



Plumularia tenuis sj). n. 



Gonosome. — The gonangia arise from the main stem, at the 

 distal ends of the internodes just below the origins of the 

 pinnae. The male gonangia are very elongated, and Avhen 

 mature are generally ridged deeply and irregularly about the 

 middle. The l:)lastostyle does not form definite gonophores, 

 but the .spermatic tissue extends along its whole length (text- 

 fig. 13, C, hi). 



Length of mature male gonangium about 0*827 nnn., 

 breadth 0"186 mm. 



The female gonangia are more ovate ; when immature they 



