S74i Prof. Allman on the Construction and 



The genus Hincksia has been constituted by Agassiz for an Austra- 

 lian Hydroid described by Mr. Hincks from the dried periderm. 

 Though there may be considerable doubt as to the justice of attri- 

 buting a generic value to the characters assumed by Agassiz as the 

 distinguishing mark of Hincksia, I have here retained the genus, 

 with the expectation that the examination of the living Hydroid will 

 confirm its title to a distinct generic rank. 



Hincksia tincta, Agass. (gen.), = Campanularia tincta, Hincks. 



5. GoNOTHYR^A*, Allman, nov. gen. 



Trophosome. — Hydrocaulus branching, rooted by a filiform 

 hydrorhiza ; hydrotheca bell-shaped, with entire or serrated 

 margin, and destitute of operculum ; tentacula surrounding the 

 base of a large, very contractile metastome. 



Gonosome. — Gonophores adelocodonic. Sporosacs in the form 

 of imperfect Medusae (meconidia), carrying round the rudi- 

 mental codonostome a circle of filiform tentacula, and, when 

 mature, supported on the summit of the gonangium, where 

 they lie entirely external to its cavity. 



Gonothyraa Loveni, Allm., = Campanularia geniculata. Lister, 

 Loven, Schultze, =s Xaomeci'efl Loveni, Allm. 



Gonothyraa gracilis, Sars (sp.), = Laomedea gracilis, Sars. 



6. Teichydra, Strethill Wright. 



Trophosome. — Hydrorhiza a branched and creeping thread, 

 which sends off at intervals a rudimental hydrocaulus in the 

 form of very short, tubular, cell-like processes, into which the 

 polypites are retractile. Polypites very slender and cylindrical, 

 carrying a single verticil of fihform tentacula round the base of 

 a short conical metastome. 



Gonosome unknown. 



The genus Trichydra has been constituted by Dr. "Wright for a 

 Hydroid whose most important characters I have endeavoured to 

 combine in the above diagnosis. I am by no means sure, however, 

 of its being a well-established genus : it forcibly suggests the imma- 

 ture condition of some other form ; and until its gonosome be dis- 

 covered, we must continue to regard it as doubtful. It is true that 

 Dr. Wright is of opinion that a Medusa of the type which we find 

 in Periffonimus, and which he met with in a vase containing speci- 

 mens of his Trichydra, may have been given off by this Hydroid ; 

 but it seems to me that the evidence is by no means in favour of 

 this view, and indeed Dr. Wright does not himself insist upon it. 

 It must be borne in mind that no trace of a gonosome was visible in 

 any of the specimens ; and I cannot avoid the belief that the Medusa 

 found in the vase was accidentally present there. The great exten- 



* From y6vQS, offspring, and Bvpalos, outside the door. 



