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 prolifer, Agass. 
4. CoryMorpua, Sars (in part). 
Trophosome.—Polypite solitary, borne on the summit of a 
simple hydrocaulus, which termmates 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 mie marginal 
tentacle always remains solitary. 
Corymorpha nutans, Sars. 
Corymorpha nana, Alder. 
5. Ama.tHea, O. 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. Medusz with a deep bell-shaped umbrella, four radiating 
canals, and four equal marginal tentacles with bulbous bases. 
Amalthea wvifera, O. Schmidt, = Corymorpha uvifera, Sars. 
- Amalthea Sarsii, Steenstrup (sp.),= Corymorpha Sarsi, Steen- 
strup. 
Amalthea Januari, Steenstrup (sp.), = Corymorpha Januarii, 
Steenstrup. 
