350 Prof. Allman on the Construction and 



defined in the present paper; the "coenosarc" is the common 

 connecting basis of the colony, and is more or less completely 

 invested by a chitinous "periderm" excreted from its surface; 

 the " hydrorhiza " (Huxley) is the root-like proximal termination 

 of the coenosarc by which the Hydroid attaches itself to foreign 

 bodies; the " hydrocaulus " is the free or (in certain creeping 

 forms) more or less adherent portion of the coenosarc, which 

 intervenes between the hydrorhiza and the polypites ; the " meta- 

 stome " is that portion of the polypite which intervenes between 

 the mouth and the most distal set of tentacles; the "hydro- 

 theca",(Huxley) is the cup-like receptacle into which the polypites 

 are retractile in the Campanularian and Sertularian Hydroids; 

 the " gonophore " is the proper generative bud, either in the 

 form of a sac or of a locomotive Medusa, upon which devolves 

 the function of giving origin directly or indirectly to the gene- 

 rative elements ; the " gonangium " is the capsule or receptacle 

 in which the gonophores are contained in the Campanularian 

 and Sertularian Hydroids; the " gonoblastidium " (Huxley) is a 

 more or less developed column which exists in certain Hydroids, 

 and is destined to give origin to the gonophores, which are pro- 

 duced as buds from its sides ; " adelocodonic " gonophores are 

 those which are constructed on the plan of the " sporosac " — 

 that is, in which the umbrella is never developed so as to pre- 

 sent a vnde orifice or " codonostome," and never becomes capa- 

 ble of acting as a locomotive organ ; " phanerocodonic " gono- 

 phores are those which present the type of the developed Me- 

 dusa in which the umbrella presents a wide orifice, and may in 

 almost every case act as an organ of locomotion. 



Synopsis of the Genera and Species of Tubularian Hydroids 

 whose trophosomes are known. 



Clavidae. 

 1. Clava, GmeHn. 



Trophosome. — Coenosarc consisting mainly of a filiform hydro- 

 rhiza entirely invested by a chitinous periderm; hydrocaulus 

 rudimental, and consisting of very short, simple, tubular pro- 

 cesses from the free surface of the hydrorhiza, invested^ like the 

 hydrorhiza, by a periderm, and carrying the polypites on their 

 summit; Polypites claviform, with scattered fihform tentacula. 



Gonosome. — Gonophores adelocodonic, sessile or on very short 

 peduncles, borne on the body of the polypite at the proximal 

 side of the tentacles. 



Clava muUicornis, Forskal (sp.), = Hydra multicomis, Forskal. 



Clti^a t^ens, Wright^ = Clava discreta, AUm. 



