106 ATRACTYLIDJS. 



DICOETNE CONFEETA grows iii dense masses on old univalve 

 shells. Its principal shoots rise to a height of about 

 half an inch and are irregularly branched. The branches 

 are erect, " ascending at a very acute angle from the 

 stem," so that the habit is slender and compact. Besides 

 the taller shoots, there are generally many short, unbranched 

 stems, bearing single polypites. These are chiefly of the 

 proliferous kind ; and I have seen a large portion of the 

 surface of the shell, over which the zoophyte was spreading, 

 densely covered with a multitude of them, heavily laden 

 with the clustering fruit. The fertile are also mingled 

 with the alimentary polypites on the larger shoots ; but in 

 the specimen to which I have referred, the latter formed an 

 inconsiderable element, compared with the thick under- 

 growth that surrounded them. 



The number of the tentacles is variable. It sometimes 

 reaches 16, but Alder gives 10 as the usual complement. 



The remarkable free zooid of ilieDicoryne is unique, so far 

 as our present knowledge goes, and is extremely interesting 

 as an intermediate form. It consists of a sexual polypite 

 (manubrium) furnished with two tentacles, which repre- 

 sent the more usual natatory organ, while simple ciliary 

 action replaces the propulsive movement of the swimming- 

 bell. It swims, according to Allman, " with its body in a 

 vertical position, carrying the posterior or tentacular extre- 

 mity uppermost, and maintaining all the time a constant 

 rotation on its longer or vertical axis." The female zooid 

 produces two ova. 



Hab. On old shells of Buccinwn undatum and Fusus 

 antiquus from deep water, Cullercoats (J. A.) : Orkney, in 

 about 3 fathoms, on an old Buccinwn undatum tenanted 

 by a Hermit Crab (G. J. A.) : Shetland, on Turritdla &c. 

 (A. M. N.). 



