HALOPTERIS CARINATA. 33 



The genus Halopterls constitutes an intermediate form between Aglao- 

 phenia and Plumularia. To Aglaophenia it shows an affinity by its 

 paired nematophores being adnate to the hydrothecae, and by its fixed 

 monothalamic mesial nematophores with slit-like aperture. To Plumularia 

 it is connected by having more than one azygous nematophore seated 

 on each internode of the pinnae, and all at a distance from the hydro- 

 theca, by the wide separation of the hydrothecaD from one another, and 

 by their even margin. 



Halopterls carinata. 



PI XIX. Figs. 3-7. 



Trophosome. — Hydrocaulus attaining a height of about two inches, 

 simple, non-fascicled ; pinnae alternate, springing one from each internode 

 of the stem, near its proximal end ; internodes of pinnae separated from 

 one another by oblique joints, each carrying a hydrotheca near its mid- 

 dle. Hydrothecae very large, adnate to internode for about two thirds of 

 their height, and then becoming free, deep, nearly cylindrical in lateral 

 aspect, infundibuliform in front aspect, margin even, with a slightly 

 prominent cusp in front, from which a slight keel is continued for some 

 distance along the front of tlie hydrotheca. Lateral nematophores in 

 the form of a long tubular stalk which springs from the internode at 

 a point near its middle, and thence passing obliquely across the side of 

 the hydrotheca, reaches the margin, where it terminates in a cup-like 

 dilatation. Mesial nematophores free, fixed by a narrow base, two on 

 each internode, one being just below the hydrotheca, and one at a 

 little distance above it. 



Gonosome not known. 



Off Carysfort Reef, from a depth of 35 fathoms. 



This is a remarkable hydroid, rendered striking by its long tubular lat- 

 eral nematophores, and by the peculiar form and large size of its hy- 

 drothecae. The stem carries between the pinnae longitudinal rows of 

 short fixed nematophores whose oblique aperture is continued into a 

 lateral slit. Though the mesial nematophores of the pinna? are attached 

 by a narrow base, they are firmly fixed, thus, along with the nemato- 

 phores of the stem, contrasting with the movable and easily detached 

 nematophores of the true Plumularia\ In this respect, and in their 

 oblique and slit orifice, they resemble the nematophores of Aglaopheniiu 



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