ORDER II. HYDROIDEA. 691 



a polyp-flower when expanded ; others are much branched ; and others 

 are short clumsy polyps. The tentacles are in one or two ranges, or 

 scattered over the summit of the animal, which is usually oblong- 

 conical, or rostriform, with a mouth and a circle of short tentacles at 

 the summit of the beak. Their structure has been developed with 

 unusual fidelity and beauty, by Van Beneden, and some of the results 

 of his investigations are given in the Appendix. The following are 

 the characters of the genera, as laid down by him : 



1. Coralligenous ; forming honn/ corolla. 



1. PENNARIA (Goldfuss). Tentacles of tico kinds, the superior scattered and in 

 I ro/rs. Sertularia of Cavolini, Pol. mar., 134, pi. 5. Plumularia, Delle Chiaje, 



Mfin., iv. 145, pi. 63, fig. 3 ; Blainville, Man., 477. Pennaria, Goldfuss; Ehrenbcrg, 

 op. cit., Gen. xlii. 



2. TUBULARIA (Pallas). Tentacles of tiro kinds, in tivo series. Pallas, Elench. 

 Zooph. ; Lamarck, ii. 124; Ehrenberg, op. cit., Gen. si. 



3. SYNOOKVXA (Ehrenberg). Tentacles alike, in several scries. Ehrenberg, op. cit., 

 Gen. xxxix. Slipula, Sars. Hermia, Johnston, Mag. Zool. and Bot., ii. 326, and Brit. 

 Zooph., 111. Coryne, Lamarck, ii. 74, and Blainv., Man. ,471. 



4. CORYDEXDRIUM (Van Beneden). Tentacles alike, scattered. 



5. EruKxuRiuM (Ehrenberg). Tentacles in one series. Ehrenberg, op. cit., G. xli. 



II. j\bl coralligenous. 



6. OOHYNA (Goertner). Tentacles alike, scattered. Hydra, Miiller, Zool. Dan.; 

 Cori/ne, Lamarck, ii. 73 ; Coryna, Blainville, Man., 471 ; Ehrenb., Gen. xxxviii. 



7. HYDRACTINIA (Van Beneden). Tentacles in a single series. Van Beneden, Bull, 

 do 1'Acad. Roy. de Bruxelles, viii., 1841, 89, pi. 1-5; and Mem. de I'Ac. Roy., xvii. pi. 6; 

 Dysmorphosa, Philippi, Zool. Beobacht., Wicgm. Arch., 1842, 33, pi. 1, figs. 2, 3; Cor- 

 dijlopliofa, Allman, Brit. Assoc., 1843, and Ann. Nat. Hist., xiii. 328; Syniiydra, Qua- 

 trefagcs, Ann. des Sci. Nat., Oct. 1843. 



TUBULARIA ORN ATA. (Couthouy.) 



T.fiUformis, 3-4" alta, polypis grandibus, rostro elongate subcylindrico, 

 tentaculis externis filiformibus, apice supernis brevissimis ; ramulis 

 gemmuliferis multiramosis. 



Filiform, 3 to 4 inches high ; polyps large ; beak long, subcylindrical ; 

 external tentacles filiform, oral tentacles very short; gemmuliferous 

 branchlets much branched, lax and pendent. 



Rio Janeiro. Exp. Exp. 



