582 RECORD OF CURRENT RESEARCHES RELATING TO 



The Geriantlilda arc separated from tlic Hexacoralla, with which 

 they are usually associated, from the fact that their sarcosepta (mesen- 

 teries) are not arranged in pairs the number of which is half that of 

 the tentacles ; in this respect they agree with the Octocoralla. 



The subdivision Corallarcha is an entirely hypothetical one, made 

 to contain the sui)posed stem-forms of the Actiuozoa, with an indeter- 

 minate number of sarcosepta (ProtocoralUda), and those in which the 

 number had become fixed at four (Tetraseptata). This latter grouj» is 

 taken to be quite distinct from the Tetractinida, the hypothetical 

 ancestors of the Bugosa, in which the number of sarcosepta was at least 

 eight. 



The author gives the following genealogical tree of the class : — 



DiASEPTIGERA. ZtGOSEPTIGEKA. 



Heterocoralla. Octocoralla. Hexacoralla. 



Tetraseptata. Tetracoralla. 



I Tetractinida. 

 I 



Protocorallida. 

 Corallarcha. 



Archydra. 



New Paludicolous Medusa.* — The Mednsce are almost exclusively 

 pelagic zoophytes, inhabiting the open sea, and they dread nothing 

 more than fresh water, which is a destructive poison to them. Even 

 brackish water kills them instantaneously. Moreover, they constantly 

 need a water rich in oxygen, fresh and incessantly renewed by the 

 perpetual movement of the waves and currents. The Medusce, in fact, 

 have an almost equal dread of fresh water, of stagnant sea-water, and 

 of a slightly too high temperature. 



All these considerations will enable the reader to understand, says 

 Dr. Du Plessis, how he was surprised, at the end of the month of 

 June, 1876, at finding, in the middle of the discharging canal of the 

 saltworks of Villeroy, near Cette, a charming Medusce. of a new species, 

 which inhabits these salt marshes in the summer. It belongs to the 

 genus Cosmetira, a section of the numerous group of the Oceanidaa ; 

 and it is curious that it is a miniature cojjy of a much larger species, 

 Cosmetira punctata, which occurs frequently in the sea near Cette, and 

 at Nice, Naples, and elsewhere. 



The interest possessed by this creature is concentrated in the novel 

 conditions to which it must have accommodated itself to be able to 

 exist in the locality where it is now met with. The canal is not more 

 than two or three metres broad, and not more than one metre deep. 

 The soil is a black putrid mud, stinking of sulphuretted hydrogen. 

 The water is perfectly stagnant and very brackish. It is without any 

 shade, is almost all day long exposed to the burning sun of Languedoc, 

 and often exceeds 77° F. 



The Medusa always inhabits the lower surface of islets of floating 



* ' Bidl. Soc. Vaiul. Sci. Nat.,' xxi. (1879) p. 39. 



