48 THE VOYAGE OF H.M.S. CHALLENGER. 
Streptocaulus, nov. gen. 
Name from orperros, twisted, and xavAds, a stem, in allusion to the torsion of the stem round its 
axis. 
Generic Coaracter. Trophosome.—Hydrocladia disposed in a continuous spiral 
round the stem. Hydrothecee with entire margin. Mesial nematophore not adnate to 
the walls of the hydrotheea. 
(ronosome not known. 
The species on which the genus Streptocaulus has heen founded is rendered very 
striking by the spiral instead of pinnate disposition of its hydrocladia. Even here, 
however, we may regard the hydrocladia as having primarily a semi-pinnate arrangement, 
or as being confined to one side of the stem, while a torsion of the stem round its axis— 
the proximal end remaining fixed—causes the hydrocladia to fall into a continuous spiral. 
So remarkable a form of ramification may well be assumed as affording a character of 
generic value. ‘The absence of serration in the margin of the hydrotheca, and still more 
the detachment of the mesial nematophore: from the hydrotheca, are also characters 
very unusual among the Statoplean Plumularide. 
Streptocaulus pulcherrimus, nu. sp. (Pl. XVI. figs. 1-8). 
Trophosome.—Colony attaining a height of about nine inches; stem simple, fascicled, 
wavy; hydrocladia nearly an inch in leneth, occupying about the distal half of the stem. 
Hydrothecee deep, thimble-shaped, margin with a single tooth-like extension in front ; 
mesial nematophore in the form of a free conical spine, with a terminal and a lateral 
aperture, springing from a point of the hydrothecal internode immediately below the 
hydrotheca ; lateral nematophores pyriform, overtopping the hydrotheca. 
The habit of this beautiful Hydroid is very different from that of every other known 
species. Among Statoplean forms it is the only species as yet discovered in which the 
disposition of the hydrocladia is not strictly pinnate. 
Dredged in Porto Praya, St Jago, from a depth of 100 fathoms. 
Diplocheilus, nov. gen. 
Nume from durAvos, double, and xetAos, a lip, in allusion to the duplicature of the hydrotheca 
margin, 
Generic Cuaracter. Trophosome.—Hydrotheca with a duplicature of its walls forming 
an external calycine envelope, which surrounds the hydrotheca for some distance behind 
the orifice. Mesial nematophore in the form of a shield-like process not adnate to the 
hydrotheca ; lateral nematophores absent. 
