BOUGAINVILLIA SUPERCILIARIS. 315 



Bouc/ainviUia fniiicosa is closely allied to BouguinvilUu ramosa. It differs from it, however, 

 ill the more cylindrical and more slender form of the extended hydranth, and in the fact that the 

 tentacles, when extended, are decidedly curved, while they are nearly straight in BougaimUlia ra- 

 mosa, as well as in the considerably less extent to which the hydranth is invested by the membranous 

 dilatation of the chitinous perisarc, and in the absence of distinct annulation at the origin of the 

 branchlcts. While in Boiif/aiiiviUla ramosa the contracted liydranths are almost entirely con- 

 cealed within the dilated perisarc, in TiougainviUia frulicosa the liydranths, in extreme retraction, 

 have the whole of the tentacles and at least half the body exposed. Another difference will, 

 perhaps, be found in the way in which the recently liberated medusa carries its marginal tentacles, 

 which in Bongainvillia fndicosa I have never seen extended in the plane of the codonostomc! 

 before bending vertically downwards, the habitual attitude of these appendages in BouyainviUia 

 ramosa. 



Whether the mature medusa differs in any respect from that of BoiiyainvUlia Britannica, 

 we have not yet facts to enable us to decide. 



I first met with Bou(/auwillia fntticosa loaded with gonophores and growing in abundance 

 on a large piece of floating timber in the estuary of the Kenmare River, Co. Kerry, and after- 

 Avards in less perfection, and without gonophores, on a buoy in the Firth of Forth. It is a 

 singularly beautiful hydroid, and when first transferred from the sea to the zoophyte trough of 

 the microscope, before its health and vigour have become impaii-ed by the confinement of our jars, 

 offers a spectacle unsurpassed in interest by any other species — every branchlet crowned by its 

 graceful hydranth, and budding with medusae in all stages of development, some still in the 

 condition of minute buds, in which no trace of the definite medusa-form can yet be detected ; 

 others, in which the outlines of the medusa can be distinctly traced within the transparent 

 ectotheque ; others, again, just casting off this thin outer pellicle, and others completely freed 

 from it, struggling with convulsive efforts to break loose from the colony, and finally launched 

 forth in the full enjoyment of their freedom into the surrounding water. I know of no form in 

 which so many of the characteristic features of a typical hydroid are more finely expressed than 

 in this beautiful species. 



*^* 3. BOTJGAINVILLIA SUPEECILIAEIS, AgaSSlZ. 



HippocRENE suPEiiciLiAiiis (mcdusa), — Agassiz, North American Acalephse, part i, pi. i — iii. 



BouGAiNviLLiA SUPERCILIARIS, — Ayassiz, Coutr. Nat. Hist. U.S., vol. iv, p. 289, pi xxvi, figs. 



1 — 7. Alex. 'Affassiz, Catal. North American 

 Acalephfe, p. 153, figs. 232—240. 



TROPHOSOME. — Htdeocaulus attaining a height of about two inches, and 

 forming clusters in which the branches are given off " rather irregularly, though more 

 or less alternately or spirally," the principal branches and ramuli more or less dis- 

 tinctly annulated at their origin. Htdb.a:nths with from fifteen to twenty tentacles, 

 strongly marked by annular clusters of thread-cells ; hypostome " very short, forming 



41 



