316 ERNEST WARREN. 



DiSTRiBUTFON. — There has been detected no character by 

 which this hydroid can be distinguished from T. tubuli- 

 f or mis, described by Nutting. The distribution given is — 

 " Dschidda (Dr. Billitzer) ; Bay of Bahia, Brazil (Rathbun) ; 

 Florida, between Salt Pond and Stock Island (Dr. E. Palmer) ; 

 Bahama Banks, 3-6 fathoms (Nutting)." The hydroid does 

 not appear to have been described from elsewhere, and its 

 occurrence on the coast of Natal gives to it a rather remark- 

 able distribution. 



(22) Plumularia tenuis sp. n. 



This delicate hydroid is common on the Natal coast. It is 

 exceedingly transparent and inconspicuous during life. It 

 grows on sea-weeds near the low-water line, and attains a 

 height of about f inch. 



Trophosome. — Hy drorhiza forms a reticulum with a strong 

 tendency for branches to come off at right angles from the 

 parent stolon. The perisarc may have an outer diffuse layei', 

 nearly double the thickness of the inner compact layer. 



Diameter of hy drorhiza about 0"162 mm. ; thickness of 

 perisarc, outer diffuse layer 33*3^i, inner layer 8'9/.«. 



Irregularly placed pegs of various shapes project into the 

 cavity of the hydrorhiza from the vertical sides. 



Hydrocaulus. — Stems divided by transverse joints into 

 internodes, each of which bears a pinna on a process from its 

 distal end. Pinna? alternate ; proximal internode very short, 

 bearing no structures, the rest of the pinna divided by oblique 

 nodes into hydrothecate internodes alternating with inter- 

 nodes bearing a nematophore only. Above and below the 

 nodes there is an internal annulation. 



Nematophores rather large, supra-calycine pair overtopping 

 the hydrotheca, a mesial nematophore at the base of each 

 hydrotheca, one at the proximal end of the intermediate 

 internodes, one in the axil of the pinna and stem, and one at 

 the basal end of each internode of main stem. Nematocysts 

 of the nematophores, length Cri) n, breadth 2*5/<. 



