HYDRANTHEA MARGARICA. 301 



HYDEANTHEA, Einchs. 



Name. — From Hydra, a genus of hydroids, and m'floc, a flower. 



TROPHOSOME. — Htdrophtton consisting of a rudiraental htdrocaulus and a 

 creeping filiform nYDROUuizA, the whole invested by a chitinous perisarc. Hy- 

 DRANTns fusiform, mouth surrounded by a circlet of filiform tentacles. 



GONOSOME. — Sporosacs crowned by a ribbed cap, and developed from the 

 hydrorhiza. 



The genus Ili/draufkea has been instituted by Mr. Ilincks for a little hydroid which he first 

 described under the name of AtracAylis mart/arica, but which he afterwards in a letter to myself 

 referred to a new genus, which under the designation of Ilydranlliea he found it necessary to 

 construct for it. There can be no doubt of the propriety of making this remarkable little hydroid 

 the representative of a new genus. From the only form with which there is any chance of 

 generically associating it — the Wrightia {Atractylis) arenosa, Alder — it is obviously separated by 

 its rudimental hydrocaulus and by the peculiarity of its gonophores. 



It is much to be desired that we had a more detailed account of the curious little hydroid 

 on which the geiuis Hi/dranihen has been founded, and more especially of the cap-like appendage 

 described as crowning the gonophores. Mr. Hincks further infoi'ms us that from the base of the 

 gonosac there " proceed four much-branched vessels, terminating near the top of it in blind 

 extremities, and immediately enclosing the ova, which fill with a dense mass the interior of the 

 cavity." He further states that he could detect no trace of a spadix. There can be no doubt, 

 however, that the branched csecal tubes which embrace the ova represent a ramified spadix. 



HtdRANTHEA MARGARICA, Eilichs. 



Atr.\ctylis MARGARic.i, — Hiucks, in Ann. Nat. Hist, for Jan., 1863, pi. ix, figs. 3, 4. 

 Hydranthea maragarica, — Hincks, Brit. Hydr. Zooph., p. 100, pi. xix, fig. 2. 



TROPHOSOME. — Rudimental htdrocaulus in the form of minute cup-like pro- 

 cesses, which spring- from the htdrorhiza, and support the hydranths and gonophores. 

 Htdranths elongate, tentacles about twenty-four in number, alternately elevated and 

 depressed in extension, every alternate tentacle having at its base a projecting cluster 

 of bean-shaped thread-cells. 



GONOSOME. — Sporosacs large, sub-globular, pedunculate, springing from cup- 

 like processes of the hydrorhiza, which are situated singly or in pairs close to the base 

 of a hydranth. 



