860 Prof. Allman on the Construction and 



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 most subsequent writers, asKrohn(Muller's Arch. 

 1853) and Gegenbaur (Zeit. f. w. Z. 1857, p. 230). 



Dujardin and the writers who have followed him have given this 

 name to a Hydroid whose trophosome is distinguished by the cha- 

 racters here enumerated ; but as it has been shown by Hincks (Ann. 

 Nat. Hist. Dec. 1862) that this form of trophosome may have two 

 very different forms of gonosome, it is necessary to break up Dujar- 

 din'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 Clado- 

 nema, that employed by Dujardin for the only form of Medusa which 

 he succeeded in tracing to a Stauridioid trophosome. 



Stauridium productum, Wright. 



5. Cladonema, Dujardin. 



Trophosome. — Coenosarc consisting of a branching or simple 

 hydrocaulus arising from a creeping filiform hydrorhiza, the 

 whole invested by a chitinous periderm. Polypites borne on the 

 summits of the hydrocaulus, clavate, with two verticils of tenta- 

 cles, each verticil consisting of four tentacles disposed in a cross, 

 — the tentacles of the proximal verticil filiform, those of the 

 distal verticil capitate*. 



Gonosome. — Gronophores phanerocodonic, developed from the 

 body of the polypite. Umbrella deep bell-shaped; manubrium 

 large, with simple mouth ; radiating canals eight, each continued 

 at the margin of the umbrella into a branching tentacle with a 

 bulbous base provided with an ocellus. 



Cladonema radiafum, Dujardin. 



6. Pennabia, Goldfuss. 



Trophosome. — Coenosarc composed of a symmetrically ramified 

 hydrocaulus, rooted by a creeping filiform hydrorhiza, the whole 

 invested by a chitinous periderm. Polypites borne on the sum- 

 mits of the branches, oviform, with two sets of tentacles — a 

 proximal set filiform and arranged in a single verticil round the 

 base of the polypite, and a distal set capitate and scattered on 

 the body of the polypite. 



Gonosome. — Gonophores phanerocodonic, developed between 

 the proximal and distal set of tentacles. Umbrella deeply ovate ; 

 .manubrium large, but not passing beyond the orifice of the 



* It will be noticed that the above description of the trophosome of 

 Cladonema is identical with that of the trophosome of Stauridium. The 

 differences between the two genera are confined to the gonosome, where 

 they are well marked. 



