Limitation of Genera among the Hydroida. 369 



one of the canals prolonged into a single marginal tentacle with 

 a bulbous base, but without distinct ocellus. 

 Hybocodon prolifery Agass. 



4. CoRYMORPHA, Sars (in part). 



TVophosome. — Polypite solitary, borne on the summit of a 

 simple hydrocaulus, which terminates proximally in a conical 

 hydrorhiza ; both hydrocaulus and hydrorhiza invested by a very 

 delicate, transparent, filmy periderm. Polypites flask-shaped, 

 with two sets of filiform tentacles, a proximal and a distal, the 

 proximal imperfectly contractile, longer and thicker than the 

 distal, and arranged in a single verticil near the base of the 

 polypite ; the distal set very contractile, forming several closely 

 placed, alternate, more or less perfect verticils behind a conical 

 metastome. 



Gonosome. — Gonophores phanerocodonic, borne 'on branched 

 peduncles, which spring from the body of the polypite at the 

 distal side of the proximal set of tentacles. The Medusa, at the 

 time of its liberation, has a deep-belled umbrella, a well-developed 

 simple-mouthed manubrium, four radiating canals, and a single 

 marginal tentacle; each of the radiating canals terminates, at 

 its junction with the circular canal, in a bulbous expansion 

 without distinct ocellus : one of these bulbs is larger than the 

 other, and from this alone the solitary tentacle is developed. 



Judging from Corymorpha nutans, it would seem that the further 

 changes undergone by the Medusa before arriving at maturity are of 

 little importance : it is especially to be noticed that the marginal 

 tentacle always remains solitary. 



Corymorpha nutans, Sars. 



Corymorpha nana, Alder. 



5. Amalthea, 0. Schmidt. 



Trophosome. — Polypites solitary, with two sets of filiform 

 tentacles, a proximal and a distal, — the proximal set very long 

 and placed in a single verticil, the distal set very short, numerous, 

 and scattered. 



Gonosome. — Gonophores phanerocodonic, borne upon pedun- 

 cles which arise between the proximal and distal sets of tenta- 

 cles. Medusae with a deep bell-shaped umbrella, four radiating 

 canals, and four equal marginal tentacles with bulbous bases. 



Amalthea uvifera, 0. Schmidt, = Corymorpha uvifera, Sars. 



Amalthea Sarsii, Steenstrup {sp.), = Corymorpha Sarsii, Steen- 

 strup. 



Amalthea Januarii, Steenstrup (sp.), = Corymorpha Januarii, 

 Steenstrup. 



