Some Northern Hydroid Zoophytes. 



221 



regularly annulated, but have never borne hydroclades nor hydrothecae. 

 Above these the nodes bear hydrothecae, and all except the lowest have 

 borne hydroclades ; but the length is exceedingly variable — from 7 mm. with 

 two hydroclades to 18 mm. with eight. The stem hydrothecae are completely 

 immersed, are arranged in two rows, one on each side of the stem, and, 

 contrary to Nutting's statement, have their distal portions inclined alternately 

 to the right and left, analogously to those on the hydroclades, although the 

 inclination is of small moment. 



The hydroclades are simple, long (up to 42 mm.), cylindrical and robust. 

 Each narrows much at the base, where it is divided by a strong constriction 

 from a short stem process. As a rule the hydroclades are alternate, but 

 occasionally two, in one case four, occur successively on the same side. No 

 internodes could be distinguished. 



The hydrothecse lie in general in four longitudinal rows, or perhaps in 

 three, at the bases of the hydroclades. The rows are not very evident at 

 first glance, for each zig-zags more or less from right to left, only half the 

 base of one hydrotheca lying in vertical line with half the bases of its 

 predecessor and successor. The hydrothecae are still more out of the vertical 

 alignment, for they incline alternately to right and left. The distal portion 

 of a hydrotheca overlaps for a short distance the proximal portion of its 

 successor in the same vertical line. The hydrothecae are altogether immersed, 

 their aperture, which is oval with the long axis horizontal, being flush with 

 the surface of the hydroclade. In shape they are saccate : wide and 

 bulging in their lower half, and thence narrowing gently to the aperture. 

 A very short chitinous tube projects upwards from the floor of the hydrotheca, 

 forming a passage between the hydrotheca cavity and the general cavity of 

 the colony. 



The gonosome is unknown. 



Dimensions. 



Stem, 



length . 



diameter 

 Hydroclade, length . 



diameter 

 Hydrotheca, depth (base to highest margin) 



greatest diameter. 



horizontal diameter of aperture 



up to 22 cms. 

 1*5 mm. 

 up to 42 mm. 

 about 1 mm. 

 0-51— 0-55 mm. 

 0-24—0-30 mm. 

 014—0-20 mm. 



Locality. — From the neighbourhood of Iceland. 



Distribution. — There are only two previous records of this species, but 

 they indicate an exceedingly wide Arctic and sub- Arctic distribution : 



