48 THE VOYAGE OF H.M.S. CHALLENGER. 



Streptocaulus, nov. gen. 



Name from ffTparroi, twisted, auJ KauAos, a stem, iu allusiuu to tlie torsion of the stem rouiiJ its 

 axis. 



Generic Chaeacteh. Trophosoiuf. — Hydrocladia disposed iu ii coutiuuous spiral 

 round the stem. Hydrotliecne with entire margin. Mesial nematophore not aduate to 

 the walls of the hydi-otheca. 



Gonosome not known. 



The species on which the genus StrciAucaulus has been 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 hj'di'otheca, are also characters 

 very unusual among the Statoplean Flumidwidce. 



Streptocaulus indcliernmus, n. sp. (PI. XYI. figs. 1-3). 



Trophosome. — Colony attaining a height of about nine inches ; stem simple, fascicled, 

 wavy ; hydrocladia nearly an inch in length, occupying aljout the distal half of the stem. 

 Hycbotheca) 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 hydrothccal iuternode immediately below the 

 hydrotheca ; lateral nematophores pyriform, uvertopping the hydrotheca. 



The habit of this beautiful Hydroid is very difierent 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. 



Dipluchedus, nov. gen. 



Name from SitAoos, double, and xe'Ao9, a lip, iu allusion to the duplicaturc of the hydrotheca 

 margin. 



Generic Character. Trophosome. — Hydrotheca with a duplicaturc of its walls forming 

 an external calycine envelope, which surrounds the hydrotheca for some distance behind 

 the orifice. Mesial nematophore in the form uf a shield-like process not adnate to the 

 hydrotheca ; lateral nematophores absent. 



