CLAVATELLA. 71 



siderable activity as soon as it reaches a tuft of coralline 

 or weed. Eleutheria keeps the mouth turned upwards 

 when it moves ; Clavatella, on the contrary, always carries 

 it below. 



The important difference in the tentacles, accompanied 

 as it is by a corresponding difference in habits and mode 

 of life, must be accounted a generic distinction, and Cla- 

 vatella, therefore, is not to be ranked as a mere synonym 

 of Eleutheria. 



Considerable diversity seems to prevail in the number 

 of the arms. I have never met with more than six, and 

 Krohii* in his very valuable paper gives the same number. 

 Claparedef, however, states that in most of his specimens 

 there were eight. Filippi J would regard this difference as 

 specific ; but of his own specimens, while a large propor- 

 tion had six arms, 15 per cent, had seven. The number 

 is so variable that it cannot be accounted a character of 

 any special significance. The radiating canals also vary 

 in number, according to the observations of Claparede, 

 but never exceed six. 



I have already pointed out the close resemblance which 

 there is between the reproductive zooid of Clavatella and 

 the alimentary polypite. In no Hydroid is the structural 

 identity of these two elements so apparent as in the pre- 

 sent species. The sexual zooid is a free polypite, with 

 the lower portion of its arms united by a membrane 

 closely investing the base of the proboscis, and the upper 

 portion furnished with a sucker-bearing fork. If the mem- 



* " Observations on the Structure and Reproduction of Eleutheria, Q.ua- 

 tref.," Wiegmann's Archiv, 18GI, p. 157. 



t Beobachtungen iiber Anatomic imcl Entwicklungsgeschichte Wirbelloser 

 Tbiere. 



^ Mem. della E. Acad. d. Sci. di Torino, (ser. 2) torn, xxiii. 



"On Clavatella, a new genus of Coryuoid polypes, and its Eeproduc- 

 tion," Ann. N. H. for Fob. 1801. 



