SIMPLICIA. 481 



We have given the general name of RHIZOSTOMA to that portion of the 

 great genus Medusa which comprises species that have no mouth opening in 

 the centre, and that appear to live by the suction exercised by their pedicles 

 or tentacula. They have four or more ovaries. The 



RHIZOSTOMA proper, 



Includes those which are furnished with a central pedicle more or less 

 ramified according to the species. 



The vessels arising from the small ramifications of the pedicles unite in a 

 cavity of its base, whence branches proceed to all parts of the umbella. 



The most common species (R. bleu, Cuvier) is found along the French 

 coast at low water : the umbella is sometimes nearly two feet in width. The 

 pedicle is divided into four pairs of arms almost infinitely forked and toothed, 

 each pedicle being furnished at the base with two auricles that are also 

 dentated ; a very fine network of vessels extends round the umbella in the 

 the thickness of its margin, this is the Pulmo Marinus of Aldrovand. 



According to the observations of Audouin and Milne Edwards, these 

 Medusae seem to live much in each others society, at least they are always 

 met with in great numbers, and swimming in the same direction with their 

 bodies obliquely inclined. 



The CEPHE^E of Peron are only distinguished from the other Rhizostoma 

 by having filaments intermixed with the dentations of the pedicle, while the 

 CASSIOPE^E, which have no pedicle, properly so called, have their arms, 

 usually eight in number, rising immediately from their inferior surface, these 

 are sometimes ramous. 



In some other species which have no central mouth, we find none of those 

 numerous ramifications in the pedicle, neither do we find open cavities for 

 lodging the ovaries ; these might be united under the name of 



ASTOMA. 



In some, however, such as the LYMMNOREA and FOVONIER of Peron, we 

 still find a large pedicle furnished on each side with fibrous filaments, which 

 may act as suckers ; while others, as the GERYONIA of Peron, are even desti- 

 tute of these filaments, but have an infundibuliform membrane at the 

 extremity of the pedicle, from the bottom of which vessels seem to arise that 

 ascend into the pedicle and spread out through the umbella, one of these 

 Medusa Proboscidalis, Forskahl, is found on the shores of the Mediterranean. 



In the ORITHYIA, Peron, this membrane is wanting, although it is possible 

 that mutilated Geryoniae, which are often in that condition, may have been 

 mistaken for Orithyise. In the 



BERENIX, Peron, 



We find there is no pedicle whatever, but the inferior surface appears to be 

 provided with little suckers along the track of the vessels : while in the 



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