222 HALECIID^E. 



principal branches also compound, pinnate, or bipinnate ; 

 pinnae alternate, placed at regular intervals, sometimes 

 themselves pinnate, jointed, the internodes short and 

 stout ; HYDROTHECjE alternate, one or a pair immediately 

 below each joint, tubular, with a plain and slightly 

 everted rim-, GONOTHEC^E borne in rows on the upper 

 side of the pinnae, (male) ovate, slender, tapering off 

 below, with a very short pedicel of about two rings; 

 (female) oblong, broad above and narrowing towards the 

 base, with a short tubular orifice at one side of the sub- 

 truncate top. 



THIS species, which is one of the commonest of the British 

 Hydroids, attains a height of from 6 to 10 inches ; it is 

 somewhat coarse in appearance, and characterized by a 

 marked angularity and stiffness of habit. The disposition 

 of the branches and pinnae is very regular and definite, and 

 they all form an acute angle with the stem from which 

 they spring. The calycles, in their simplest condition, 

 consist of a single tubular piece articulated to a projection 

 from the stem ; in older specimens, however, they are 

 made up of several such pieces, which fit into one another 

 and mark the successive generations of polypites. 



The principal stems are composed of a multitude of 

 extremely delicate tubules, agglutinated together, as 

 many as a hundred strands combining in the main trunk 

 of the zoophyte. Some of these diverge at regular inter- 

 vals to form the larger branches and the pinnse, and the 

 stem is thus gradually attenuated upwards, until at the 

 apex it runs out to a fine point. The polypites are large, 

 elongate, somewhat fusiform, and have rather thick ten- 

 tacles. 



Hab. On shells, stones, &c., in both shallow and deep 

 water, but more usually the latter; very common and 

 generally distributed. 



