Limitation of Genera among the Hydroida. 351 
Clava leptostyla, Agass. 
Clava diffusa, Allm. 
Clava cornea, Wright. 
Clava membranacea, Wright. 
Clava nodosa, Wright. 
Though the three species, C. cornea, OC. membranacea, and C. 
nodosa are described as Scottish, I have not seen any specimens of 
them, and I here give them on the authority of Dr. Wright. 
2. Tuprcnava, Allman. 
Trophosome.—Ccenosare consisting of a well-developed hydro- 
caulus in the form of simple or branched stems, which are given 
off at intervals from a creeping filiform hydrorhiza, the whole 
invested by a chitinous periderm. Polypites borne on the 
summit of the hydrocaulus, claviform, with scattered filiform 
tentacula. 
Gonosome.—Gonophores adelocodonic, consisting of clusters 
of sporosacs sessile on the body of the polypite at the proximal 
_ side of the tentacula. 
From the above definition the Tudiclava cornucopia of Norman * is 
excluded, this Hydroid being, in my opinion, the type of a new 
genus, which is distinguished from Tudiclava by having its gono- 
phores borne on distinct gonoblastidia, and which, I believe, Mr. 
Norman will himself shortly characterize. 
Tubiclava lucerna, Allm. 
3. Campaniciavat, Allman, nov. gen. 
Trophosome.—Ccenosarc a creeping, filiform, ramified hydro- 
rhiza invested by a periderm; hydrocaulus undeveloped. Poly- 
pites sessile on the hydrorhiza, claviform, with scattered filiform 
tentacula. 
Gonosome.—Gonophores phanerocodonic, sessile on the creep- 
ing hydrorhiza. Umbrellaat the time of its liberation deep bell- 
shaped ; manubrium simple-mouthed, shorter than the height of 
the bell-cavity ; radiating canals four; marginal tentacles two, 
continuous with two opposite radiating canals, and having bul- 
bous bases without distinct ocellus; two intervening smaller 
bulbs corresponding to the termination of the other two radiating 
canals in the circular canal. 
There can be no doubt that the Medusa here described undergoes 
further changes before arriving at maturity. It is, at least, almost 
certain that two additional marginal tentacles become developed, 
* See Norman in Ann. and Mag. Nat. Hist. Jan. 1864. 
+ Campana, a bell, and Clava, the name of a genus of Hydroids. 
