BRITISH ZOOPHYTES. 41 



water was, at any rate occasionally, salt or brackish. 

 It was discovered almost simultaueously in England 

 and Belgium. Since that time, 1854, the animal has 

 in many places migrated into rivers. At one time it 

 took possession of the great water-pipes of Hamburg 

 in such quantities as to impede the flow of water 

 through the pipes." 



Prof. Allman,* Van Beneden, and Dr. Schultze have 

 exhaustively studied this species. 



FAMILY II. HYDRACTINIID^. 



Polypites claviform, sessile, with a single verticil of 

 filiform tentacles round the base of a conical lorohoscis 

 home on an expanded and co7itinuous crust j the coeno- 

 sarc naked above. — T. H. 



Genus I. Hydractinia, Van Beneden. (Hydra, and 

 Actinia, a sea anemone.) 



Generic chai'acter contained in that of family cha- 

 racter. Reproduction by means of fixed sporosacs 

 borne usually on partially developed polypites which 

 are destitute of tentacles, but bear clusters of thread 

 cells around the oral extremity. — T. H. 



1. H. ECHiNATA, Fleming. 



Alcyonium echinatum {Fl, Do B.), Alcyonidiura 

 echinatum [G. J., B. Q. C), H. lactea and H. rosea 

 (F. B.), Echinochorium clavigerum [Has.), Synhydra 

 parasites (Quatrefages) , H. polyclina {Jg.).f 



Hab. : Generally distributed on old univalve shells 



* " Gymnoblastic Hydroids." 



t Mr. Hincks considers this to be the same species as H. 

 echinata. Prof. Allman, though with some hesitation, considers 

 the species distinct. 



