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. Globiceps, Ayres. 



TVophosome. — Coenosarc 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. 



ClavatellidaB. 

 1. Clavatella, Hincks. 



TVophosome. — Ccenosarc composed of a filiform branching 

 bydrorhiza, 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- 

 dusse, 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 Meutheria of Quatre- 

 fages, is nevertheless generically distinct from it. 



Clavatella proli/era, 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. !f Mag, N, Hist. Ser. 3. Vol. xiii. 21 



