Limitation of Genera among the Hydroida. 365 



5. Heterocordyle*, Allman, nov. gen. 



Trophosome. — Coenosarc 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, AUm. 



6. Perigonimus, Sars. 



Trophosome. — Coenosarc 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 

 coenosarc. 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 iu 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.),= Air acty lis repens, Wright. 



Perigonimus sessilis, Wright (sip.), — Atractj/lis sessilis, Wright. 



Perigonimus palliatus,'Wright (sp.), = Atractylis palliata,Wrgt 



Perigonimus ? linearis, Alder (sp.), = Atractijlis linearis, Alder f- 



Perigonimus serpens, Allman. 



Perigonimus minutus, Allman. 



Perigonimus pusillus, Wright (sp.), = Eudendrium pusillum, 

 Wright. 



7. BouGAiNviLLiA, Lcsson. 



Trophosome. — Coenosarc consisting of a branching hydro- 



* From erepos, dissimilar, and KophvKr}, a club. 



t 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. 



