248 Van Beueden on the genera Eleutheria and Synhydra. 



Just before the publication of my memoir I received the num- 

 ber of the ' Aunales des Sciences Naturellcs ' for October 1843, 

 which contains a memoir by j\I. de Quatrefages on the Synhydra 

 parasitica, a new genus of poh-]D alhed to Hydra. M. de Quatre- 

 fages has observed this polyp several times at Saint -Vast-la 

 Houque (on the coast of Normandy), and once at Brehat, on the 

 coast of Brittany. This is again the same animal as oux Hydr actinia, 

 and we are surjn'ised that this identity with the animal which we 

 had already figured in 1841 has escaped M. de Quatrefages, 



If it is true (and we for our part do not doubt it), that in 

 the Synhydra the supposed ovigerous indi^■iduals have no mouth, 

 it is only the repetition of what we see in the Campamdaiice and 

 in other polj^s. There are in fact in this genus compartments 

 which contain only a part of the common substance in which the 

 eggs are formed, and that part has been also regarded, but 

 wi'ougly, as female indiWduals without tentacles. The sole dif- 

 ference in this case is, that the stem, instead of being erect and 

 ramified as in the Campanularice, is spread horizontally, forming 

 a crust, from the surface of which both the tentaculated polyps 

 and the fleshy bodies which produce the eggs rise. It is M. de 

 Quatrefages who observed that the mouth is wanting in those 

 which have eggs. But this fact is not general among the polyps 

 of this family ; in the Corynes the indi\dduals which bear eggs 

 are as perfect as the others. 



Our observations on Hydractinia scarcely agree with those of 

 M. de Quatrefages on the Synhydra, although it may be the 

 same animal, especially in all that regards reproduction. We 

 shall soon have occasion to return to this subject. The difference 

 in our results probably arises from my ha\'ing devoted more time 

 in the investigation of the embryogeny of these animals in dif- 

 ferent genera. 



The following is the synonymy of the new genus : — 



HYDRACTINIA. 



Hydractinia, Van Beneden, Recherches sur la Structure de I'CEuf 

 dans un nouveau genre de Polype. {Hydractinie), (Bulletin de 

 I'Academie Royale de Bruxelles, torn. viii. 1841, p. 89. p]. 1 — 5.) 

 Recherches sur rEmbryogenie des Tubulaires. (Memoires de 

 I'Academie Royale de Bruxelles, torn. xvii. pi. 6.) 



Dysmorphosct, Philippi, Zoologische Beobachtungen, Wiegmann's 

 Archiv, 1842, p. 33. pi. 1. fig. 2—3. 



Cordylophora, Allman, Synopsis of the genera and species of Zoo- 

 phytes inhabiting the fresh waters of Ireland, British Association, 

 Thirteenth Meeting held at Cork in 1843. [Inserted in Ann. Nat. 

 Hist. vol. xiu. p. 328.] 



Synhydra, Quatrefages, Memoire sur la Synhydre parasite. Annales 

 des Sciences Naturelles, Octobre 1843. 



