INTRODUCTION. 



Family VIII. Sertulariidae. 



SERTULARELLA, Gray. | HYDRALLMANIA, Hincks. 

 DIPHASIA, Agassiz. " THUIARIA, Fleming. 



SERTULARIA, Linn. 



Family IX. Plumulariidse. 



ANTENNULARIA, Lamk. 

 AGLAOPHENIA, Lamx. 



PLUMULARIA, Lamk. 



Suborder III. GYMNOCHROA. 



Hydroida destitute of polypary ; locomotive. 



Family I. Hydridse. 

 HYDRA, Linnaeus. 



Agassiz, on the strength of observations made on the 

 Millepora alcicornis, Linn., proposes to transfer to the Hy- 

 droida the coral-making group of the Tabulata, which has 

 hitherto ranked amongst the Actinozoa. He also conjec- 

 tures that the Rugosa of Milne-Edwards belong to the 

 class Hydrozoa. 



