AND SPECIES OF HYDnOIBA. 279 



of the mesial line in front to a point about halfway between tiie 

 anterior and posterior walls of the hydrotheca ; mesial nemato- 

 phore very long, adnata to the whole height of the anterior wall 

 of the hydrotheca, and then extending for a distance about equal 

 to the length of its aduate portion as a free, gently recurved, hol- 

 low spine, with a lateral as well as a terminal orifice. 



Gonosome. Not known. 



Locality. Ceylon, Mr. Holdswortli. 



This is a beautiful species ; its long flexile and eminently 

 graceful plumes grew in rich masses over the stems of another 

 large JLydiroid.{IIalicornaria hipinnata). In some of the specimens 

 examined an imperfect septum was apparent, stretching across 

 the cavity of the mesial nematophore at a little distance from its 

 terminal orifice. This, however, was by no means of constant 

 occurrence. The opposite, instead of alternate, disposition of the 

 pinuffi on the common stem is a condition of very rare occurrence 

 among the Plumulariidse. 



As no gonosome was present in any of the specimens examined, 

 the reference of the species to Halicornaria is provisional ; the 

 general character of the hydrothecaB, however, belonging as these 

 do to the macrorynchial type, renders it probable that the species 

 is correctly allocated to Halicornaria. 



Halicornaria bipinnata. Plate XXIIl. fig. 2, Plate XXII. fig. 5. 



Troj^liosome. Hydrocaulus attaining a height of upwards of a 

 foot, fascicled, rooted by a dense sponge-like mass of entangled 

 fibres, strong and thick at its origin, where it measures about a 

 quarter of an inch in diameter, and soon thinning away as it be- 

 comes irregularly branched ; branches mostly in the same plane, 

 sending off along their whole length rather closely set, short, 

 alternate pinnte, which are destitute of hydrothecse, and along 

 the intervening spaces short, slender, hydrotheca-bearing pinnae ; 

 non-hydrotheca-bearing pinnae rigid, fascicled at their origin, 

 thinning away and becoming monosiphonic towards their distal 

 extremities, carrying very short secondary, alternate, mono- 

 siphonic hydrotheca-bearing pinupe, each secondary pinna spring- 

 ing from a short internode of the primary pinnae. Hydrothecae 

 closely set, deep, with the anterior wall deeply involuted below 

 the orifice, which is directed forward ; margin of orifice extended 

 in the form of a broad wing-like cheek on each side ; intrathecal 

 ridge situated near the base of the hydrotheca, and extending 



