AND SPECIES OF HYDKOIDA. 277 



the type of Plumularia setacea, Linn, With our present more 

 extended knowledge of tlie Plumulariidse, however, it must be re- 

 stricted to species which, with a trophosome formed on the general 

 type of Aylaophenia pluma, have their gonangia never included in 

 corbulfe, or connected in any way with the special gonangial ramuli 

 which in certain other species we find developed for their pro- 

 tection. 



Dr. Kirchenpauer, in his valuable memoir on the genus Agla- 

 ophenia, institutes under the name of Macrorynchia a subgenus 

 for certain forms with unprotected gonangia, giving, however, as 

 the chief character of the group, the great development of the 

 free portion of the mesial nematophore, and its being provided 

 with a lateral as well as a terminal orifice. This condition of the 

 mesial nematophore, however, we have seen to exist in a true 

 corbula-bearing species {Aglaopheiiia acantJiocarpd) ; and it pro- 

 bably occurs in many others besides those which Kirchenpauer 

 would refer to his subgenus Macroryncliia. The genus Halicor- 

 naria would include not only the forms embraced by Kirchen- 

 pauer in his Macrorynchia group of Aylaophenice, but others, 

 which, with unprotected gonangia, do not possess the double- 

 mouthed nematophore. 



Halicornaria saccaria. Plate XV. fig, 4, and Plate XXII. 

 figs. 1, 2. 



Tropliosome. Hydrocaulus attaining a height of about 9 inches, 

 rooted by a spongy mass of entangled filaments, much and very 

 irregularly branched, fascicled, very thick towards the base, and 

 thence gradually thinning away as the polysiphonic condition 

 becomes less and less, until towards their distal extremities the 

 branches have entirely lost their fascicled condition and become 

 monosiphonic ; pinnae alternate, arising from the anterior sur- 

 face of the rachis. Hydrothecse with the orifice directed forward ; 

 margin waved, but not dentate ; anterior walls deeply inflected 

 just below the orifice ; intrathecal ridge rudimenfcal ; mesial nema- 

 tophore adnate to the hydrotheca for about half the height of 

 the hydrotheca, and then forming a rather long, stout, free spine, 

 having, besides its terminal aperture, a lateral one on its upper 

 side close to the point where it becomes free ; lateral nemato- 

 phores nearly cylindrical, long, extending beyond the orifice of 

 the hydrotheca ; a double cauline nematophore just below the 

 origin of each pinna. 



Gonosome. Gronangia borne singly on a sliort pinna, which 



20* 



