70 bulletin: museum of compakative zoology. 



p. 86). In Aurelia margiualis the gonads are very l;u"ge and occupy at least 

 one half of the whole diameter of the disk, so that the distance from the peri- 

 pheral outline of these organs to the margin of the disk is as great, if not 

 greater, than that to the centre of the disk. The mouth-arms, on the contrary, 

 are comparatively small. In Aurelia habanensis the gonads never occupy more 

 than one third of the diameter of the disk, and the mouth-arms are long and 

 slender. 



CHARYBDEA, Peron and Lesdeue, 1809. 

 Charybdea aurifera, nov. sp. 



Figs. 81-83, Plate 35. 



Specific Characters. — Young medusa. Only one specimen of this medusa 

 was found at the Tortugas, Florida, August 6, 1898. The bell was 2 mm. in 

 height and a little higher than if was broad. The external surface of the bell 

 was covered irregularly with numerous wart-like clusters of nematocyst cells. 

 The 4 interradial tentacles were evidently very immature, and consisted of 

 small knob-like protuberances from the bell margin. They were hollow and 

 were in communication with the general gastro-vascular cavities of the bell. 

 The 4 sense-organs, or rhopalia, arose from 4 radially situated niches, found 

 upon the sides of the bell at a little distance above the margin. It should be 

 noted, however, that although the rhopalia appear to arise at some distance 

 above the bell margin, they are morphologically homologous with appendages 

 of the bell margin. Each rhopalium arises from a niche in the side of the 

 bell, and consists in a stalk-shaped body, bearing upon its distal end a knob- 

 shaped portion which, in turn, contains the otolith and eye-spots. There are 

 5 eyes in each rhopalium; one of these is large and median, and the other 

 4 are smaller and paired (see Figures 82, 83). They are so situated that 

 they may look inward towards the bell cavity. These eyes are ectodermal 

 structures, and possess a lens and a layer of pigment cells. The otolith, on the 

 other hand, is entodermal in origin and consists in a mass of glistening white 

 granules. The velarium is well developed, and is supported by means of 4 

 partitions, or frenulae (/, Figure 81), that suspend it from the sub-umbrella. 

 The proboscis is wide and flask-shaped, and there are 4 quadratic lips. 4 long 

 ga.'^tric cirri, one in each interradius, extend downwards into the stomach cavity. 

 A highly refractive band of muscle fibres ? (m s, Figure 81) extend down the 

 middle line of each radius of the bell to the rhopalia. The gelatinous sub- 

 stance of the bell possesses a bluish tinge. The nematocyst cells of the ex- 

 umbrella, and also the proboscis, rhopalia, and tentacles are of a decided 

 amber color. 



Although careful search was made for them, no velar canals were observed. 

 It is probable that these may develop at a later stage. 



