﻿206 



PROCEEDINGS OF THE 



[April, 1857. 



PERSA INCOLORATA, nov. spec. 

 PL 12, Fig. 3. 



The form is deeply campanulate, or thimble-shaped, rounded 

 above; widening- very gradually downwards. Bell-wall, thin, 

 except just above the digestive trunk, where it thickens to form a 

 low pedestal for the digestive trunk. Digestive trunk, cylindrical, 

 transparent, parted at the mouth into four labial tentacula, rather 

 long for the group, each furnished with a little knot of thread-cells, 

 on its inner margin, not far from its free extremity. These labia, 

 when folded back, have an appearance like that represented by 

 Gegenbaur in Trachynema ciliatum. This is the only mature 

 medusa I have seen 'with a wholly colorless digestive cavity. 

 The radiate tubes are extremely delicate; I could not trace them 

 into the digestive cavity. The sexual glands were placed a little 

 below the mid-height of the bell. They were large and rounded 

 at their poles. The ova observed in one specimen were large, 

 like those figured in Saphenia. The sexual organs were the only 

 distinctly colored portion of the animal; they were of a pale yel- 

 low color. The margin of the bell was set all round with thickly 

 crowded (thread-cell bearing?) nodes, which took the place of 

 tentacula. I never saw these exhibit any disposition to stretch out 

 their lashes, if they possessed them. The marginal vesicles were 

 all small, and of two kinds; a larger sort had each a single round 

 light-refracting corpuscle. Between every two of this kind was 

 another smaller, and containing a less transparent corpuscle, of a 

 somewhat granular appearance. If the capsules in Circe are as 

 small as these, and as closely couched among the tentacular 

 knobs upon the margin, they may very well have been overlooked 

 by Forbes. There is a slight break in the chain of tentacular 

 nodes at each point, where there is placed one of these sense 

 capsules. The vail is voluminous and was always turned within 

 the cavity of the bell, during my observation, and the numerous 

 folds into which it was thrown, obscured the view of the other side 

 of the bell-margin. 



I have seen but three specimens of this Medusa of different 

 sizes, but no one had more than two sexual glands, nor even a 

 trace of more, as is the case with Eucope, when similarly defi- 

 cient. These specimens had the exterior of the disk so beset with 

 minute Diatomaceee and Desmidiacese at the time of observation, 

 that they were thrown into a state of contraction by them, and the 

 bell acquired a certain obscurity which rendered it impossible to 



