34 
THE VOYAGE OF H.M.S. CHALLENGER. 
hydro thecae and non-differentiated hydrotheca- cavity. To this I have assigned the 
name of Halisiphonia. A remarkable example of it is contained in the collection of the 
Challenger. 
The collection contains two species of the genus Lafoea as limited by the diagnosis 
here given. Notwithstanding some differences of habit, I cannot find grounds for 
separating them from the Lafoea dumosa and Lafoea fruticosa of the European seas. 
Lafoea dumosa, Fleming, sp. (PI. XV. figs. 1, la). 
Sertularia dumosa, Fleming, Edin. Phil. Journ., vol. ii. p. 83. 
Lafoea dumosa, Hincks, Brit. Hydroid Zooph., p. 200, pi. xli. fig. 1. 
Trophosome. — Hydrocaulus free, slender, irregularly branched, main stem and 
principal branches becoming monosiphonic distally. Hydrothecae springing from all 
sides of the stem and branches, tubular, with the axis curved away from the stem, 
gradually narrowed towards the base into a short ill-defined peduncle of attachment. 
Gonosome not known. 
Locality. — Station 23, off Sombrero Island, West Indies ; depth, 450 fathoms. 
This is a very slender form, of delicate habit, and quite destitute of the vigorous 
growth by which some of the other species of Lafoea are characterised. The specimen 
has a height of about two inches. The hydrothecse are deep and rather wide, but towards 
the base become gradually namnved into a short peduncle, which is so imperfectly 
defined that the hydrothecse may almost be regarded as sessile. The branches in their 
monosiphonic portion present here and there a shallow 7 , scarcely recognisable, constriction, 
but there are no true joints dividing them into internodes. 
Apart from its more slender form and delicate habit, the present Hydroid possesses 
no character which would afford grounds for its separation from Lafoea dumosa ; and as 
these differences seem to lie within the limits of variation of a species, I believe we must 
regard it as specifically identical with the European form. 
» 
Lafoea fruticosa, Sars (PI. XVI. figs. 2, 2a). 
Lafoea fruticosa, Sars, Bemaerk. over fire norske Hydroider, Vidensk. Forhandl., 1862. 
Lafoea fruticosa, Hincks, Brit. Hydroid Zooph., p. 202, pi. xli. fig. 2. 
Trophosome. — Stem free, attaining a height of upwards of three inches, profusely 
branched, branches mostly in one and the same plane, primary branches irregular, closely 
set with pinnately disposed alternate ramuli, which are themselves for the most part 
set with secondary pinnae. Hydrothecae springing irregularly from all sides of the 
hydrocaulus, deep and narrow, with the axis gently curved away from the supporting 
stem, gradually narrowing into a loosely twisted peduncle. 
