374 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. Gonotuyr#a*, Allman, noy. 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. Sporosaes in the form 
of imperfect Medusee (meconidia), carrymg 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. 
Gonothyrea Lovéni, Allm., = Campanularia geniculata, Lister, 
Lovén, Schultze, = Laomedea Lovéni, Allm. 
Gonothyrea gracilis, Sars (sp.), = Laomedea gracilis, Sars. 
6. Tricnypra, 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 filiform 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 Perigonimus, 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 % 
z 
found in the vase was accidentally present there. The great exten- — 
A 
* From yévos, offspring, and 6upaios, outside the door, 
