292 DICORYNIDiE. 



closely aggregated along the tentacle. It is in this retracted state that the tentacular appendages 

 have been represented by Alder in his figure of this species. 



DIC0RYNID.1J. 



TROPHOSOME. — Hyduocaulus developed, invested by a perisarc. Htdranths 

 with verticillate tiliform tentacles. 



GONOSOME. — GoNOPUORES in the form of natatory ciliated sporosacs, with two 

 simple, ciliated basal tentacles. 



DICORYNE, Allman. 



Name. — Sic, double, and /copu'i'ij, a club ; so called from its two club-shaped zooids — the hydranth 



and the blastostyle. 



TROPHOSOME. — Hydrocaulus consisting of branched or simple stems, which 

 arise at intervals from a creeping filiform hydrorhiza. Hydranths fusiform, with 

 a single circlet of filiform tentacles surrounding the base of a conical hypostome. 



GONOSOME. — Sporosacs developed upon blastostyles, detaching themselves as 

 natatory planoblasts, ciliated over their entire surface, and having two filiform tenta- 

 cles diverging from the proximal end. 



The very remarkable sporosacs of Bicoryne separate it by a wide interval from every other 

 genus. These sporosacs when mature become free, and lead a life as natatory as that of a 

 medusiform planoblast. Natation, however, is effected not by the systole and diastole of an 

 luubrella, but by the vibration of the cilia with which the entire surface of the sporosac is clothed. 

 So important are these characters, that Bicoryne must become the type of a distinct family of 

 gymuoblastic hydroids. 



