~ 
Limitation of Genera among the Hydroida. 365 
5. Hererocorpyie*, Allman, nov. gen. 
Trophosome.—Ceenosare consisting of a simple or branched 
hydrocaulus, which arises from a creeping, filiform and anasto- 
mosing hydrorhiza, the whole invested by a chitinous periderm. 
Polypites fusiform, with a single verticil of filiform tentacula 
round the base of a conical metastome. 
Gonosome.—Gonophores adelocodonic, borne by gonoblastidia, 
which are developed (solely ?) from the hydrorhiza ; sporosacs of 
the ordinary kind, destitute of tentacles and cilia, and incapable 
of locomotion. 
Heterocordyle Conybearei, Allm. 
6. Puriconrmus, Sars. 
Trophosome.—Ccenosare invested by a periderm, and consist- 
ing of a branching or simple hydrocaulus rooted by a filiform 
hydrorhiza. Polypites borne on the summits of the hydro- 
caulus, fusiform, with a single verticil of filiform tentacula, which 
surround the base of a conical metastome. 
Gonosome.—Gonophores phanerocodonic, developed from the 
ccenosare. Umbrella at the time of liberation deep bell-shaped, 
with a manubrium which is shorter than the height of the bell- 
cavity, and has a mouth which is simple or with four shallow 
lips ; radiating canals four; marginal tentacles two or four, with 
bulbous bases, which are not furnished with distinct ocelli. 
The changes which occur as the Medusa advances towards matu- 
rity are to be chiefly sought for in an increase in the number of 
marginal tentacles, the new tentacles being intercalated at the middle 
point between every two older ones. 
Perigonimus muscoides, Sars. 
Perigonimus repens, Wright (sp.),=Atractylis repens, Wright. 
Perigonimus sessilis, Wright-(sp.),= Atractylis sessilis, Wright. 
Perigonimus palliatus, Wright (sp.),= Atractylis palliata, Wrgt. 
Perigonimus? linearis, Alder (sp.),= Atractylis linearis, Alder +. 
Perigonimus serpens, Allman. 
Perigonimus minutus, Allman. 
Perigonimus pusillus, Wright (sp.), = Eudendrium pusillum, 
Wright. 
7. BouUGAINVILLIA, Lesson. 
Trophosome.—Ccenosare consisting of a branching hydro- 
* From érepos, dissimilar, and kopdvAn, a club. 
+ It is with some doubt that I place this species in the genus Perigoni- 
mus, the Medusa having been apparently examined in imperfect specimens, 
and consequently not determinable with sufficient certainty from Mr. Alder’s 
figure and description ; but it seems to come nearer to the type which is 
characteristic of Perigonimus than to anything else. 
