Limitation of Genera among the Hydroida. 361 
umbrella ; radiating canals four; four rudimental, papilliform 
marginal tentacles*, 
Pennaria distycha, Goldf., = Pennaria Cavolini, Ehrenb., = 
Sertularia pennaria, Cavolini. 
Pennaria gibbosa, Agassiz. 
7. Grosicers, Ayres. 
Trophosome.—Ccenosare rooted, symmetrically branched, and 
invested by a chitinous periderm. Polypites claviform, with two 
sets of tentacles—a proximal set filiform and arranged in a single 
verticil round the base of the polypite, and a distal set capitate 
and arranged in one or more verticils, never scattered. 
Gonosome.—Gonophores phanerocodonic, developed between 
the proximal and distal sets of tentacles. Umbrella deeply ovate, 
with large manubrium; four radiating canals, and four rudi- 
mental, papilliform marginal tentacula. 
Globiceps tiarella, Ayres, = Eucoryne elegans, Leidy, = Pen- 
naria tiarella, M‘Crady. 
Clavatellide, 
1, Cuavateia, Hincks. 
Trophosome.—Ccenosare composed of a filiform branching 
hydrorhiza, with a hydrocaulus consisting of very short simple 
stems, which arise from the free surface of the hydrorhiza, the 
whole invested by a periderm. Polypites developed from the 
summit of the hydrocaulus, and having a single verticil of 
capitate tentacula surrounding the base of a conical metastome. 
Gonosome.—Gonophores consisting of naked ambulatory Me- 
dusze, which are developed in clusters from the polypite near its 
proximal extremity. Umbrella not extended into a bell or disc 
fitted for natation; marginal tentacles six, bifurcated, the outer 
branch of the bifurcation terminated by a capitulum of large 
thread-cells, the inner by a claviform enlargement which carries 
a suctorial disk of attachment; an ocellus at the root of each 
tentacle ; no lithocysts. 
Clavatella, though it comes very near to the Eleutheria of Quatre- 
fages, is nevertheless generically distinct from it. 
Clavatella prolifera, Hincks. 
_ * Agassiz describes, but not without doubt, the generative elements as 
produced upon the radiating canals. I entirely participate in Agassiz’s 
doubts on this point. From Cavolini’s description, it is plain that in his 
species the generative elements were produced in the walls of the manu- 
brium, as in all other known cases among the Tabularian hydroids, 
Ann. & Mag, N. Hist. Ser, 3. Vol, xiii. 24 
