ZYGODACTYLA. 191 



The gonozooid of C. turrita, as I learn from Professor 

 Wyville Thomson, who has kindly supplied me with the 

 drawing on which this description is founded, resembles 

 that of C. acuminata so closely that it is difficult to distin- 

 guish the one from the other. It is slightly broader in its 

 proportions and perfectly colourless. The umbrella is 

 dotted over with large thread-cells. 



Hab. Very abundant on Zostera (along with Campanu- 

 laria angulata], Holy wood, Belfast Lough (Prof. W. 

 Thomson) . 



Genus ZYGODACTYLA, Brandt. 



JEQroEEA, Peron and Lesueur (in part). 

 RHACOSTOMA, Agassiz. 



GENERIC CHARACTER. Stem simple or branching, rooted 

 by a filiform stolon ; hydrothecce with an operculum formed 

 of many convergent and acuminate segments; polypites 

 cylindrical, with the tentacles ivebbed below. Reproduction 

 by free medusiform zooids. 



Gonozooid : Umbrella (in the adult] more or less hemi- 

 spherical ; manubrium short, ivith many fimbriated lips ; 

 radiating canals very numerous; marginal tentacles very 

 numerous, with bulbous bases ; lithocysts borne on the 

 margin of the umbrella. 



THE medusiform sexual zooids of several Zygodactyla; 

 are known, but in one case only has the polypite been ob- 

 served. The gonozooids are remarkable for their size; 

 those of Z. Grcenlandica (A. Agass) sometimes measure as 

 much as fifteen inches in diameter ; those of Z. crassa, of 

 the same author, are nearly as large. 



The number of radiating canals in the adult is very great 

 (about 100) ; they are progressively developed; and in very 

 young specimens, according to the observations of A. 



