370 STAURIDIUM. 



distinct genus. Indeed, the principles which have guided us in the definition of genera among 

 the Hydroida would not justify the association of the present hydroid, in a single genus, with 

 the " Sertidaria pennaria" of Cavolini. 



As in Pennaria CavoKnii, the generative elements are not only developed in the walls of 

 the manubrium, but the ova may even attain the condition of planulae before the liberation of 

 the medusa. M'Crady, however, has seen the medusa become free before the escape of the 

 planulae. 



STAUEIDIUM, JDiijardin. 



Name. — From aTav^uq, a cross ; in allusion to the cross-like disposition of the tentacles in 



the hydranth. 



TROPHOSOME. — Htdrophyton consisting of a simple or irregularly branched 

 nTDROCAULUs arising from a creeping filiform nTBROUHizA, the whole invested with a 

 PEEiSAEC. Hydranths clavate, with one or more verticils of capitate tentacles, and 

 one verticil of filiform tentacles, the tentacles in each being four in number and 

 disposed in a cross ; the verticil of filiform tentacles placed at the proximal side of 

 the others. 



GONOSOME. — Planoblasts developed from the body of the hydranth. Umbrella 

 deep bell-shaped ; manubrium with the mouth simple ; marginal tentacles four, 

 nodulated with clusters of thread-cells, and having a distinct ocellus on the basal bulb. 



The name Slauridium is the same as " Staiir'uUe" of Dujardin, only with its termination 

 altered so as to adapt it to the ordinary form of zoological nomenclature, a form in which 

 Dujardin's name has been used by subsequent writers, as Krohn, Gegenbaur, and Wright. 



Dujardin and the writers who have followed him have given this name to a hydroid whose 

 trophosome is distinguished by the characters just enumerated ; but as it has been shown by 

 Hincks that this form of trophosome may have tw^o very different forms of gonosome,* it is 

 necessary to break up Dujardin's genus into two, one of which may retain his original name for 

 the trophosome, while to the other we may give the name of Cladonema, that employed liy 

 Dujardin for the only form of medusa whicli he succeeded in tracing to a Stauridioid 

 trophosome. 



We are indebted to Ilincks for a description of the medusa of the present genus. He has 

 called attention to the important morphological fact that it is in every respect identical with that 

 of the very different hydroid, Sj/ncorj/ne exiutiur 



1 Hincks, in ' Ann. Nat. Hist.' for Dec, 180,3. 

 " Loc. cit. 



