MEDUSA, 143 



PSYTHIA, gen, nov. 



"W'illiadjB with four simple unbninched radial canals. 



In all previously known genera of the family Williadte the radial canals 

 are branched. The general form, color, shape of proboscis, and method of 

 budding of the pre.sent medusa, however, all incline one to place it among 

 the Williadi-e. It may be a primitive, or ancestral, form in wliich the canals 

 have remained simple, or possibly an atavistic sport from some of the more 

 complex Williadte, or an immature individual which may give rise to 

 medusa-bud^ before attaining its complete development. 



Psythia prolifera, sp. nov. 



Plate i, fig. 3. 



In the single specimen obtained, the bell was much shrivelled by con- 

 traction, so that its exact shape could not be ascertained. It appeared, 

 however, to be slightly flatter than a hemisphere, and 4 nun. in diameter. 

 The gelatinous substance Avas of uniform and only moderate thickness. 

 There were four stiff, radially situated tentacles, each of which was about 

 one-half as long as the bell-lieight. The entoderm of these tentacles was 

 composed of choidate cells, and a very fine iixial canal appeared to extend 

 throughout the length of each tentacle. There were four straight, simple, 

 radial canals; and a simple, slender, circular canal. The proboscis was 

 cruciform in cross-section, and about three-quarters as long as the height 

 of the bell-cavity. The four lips were small and slightly recurved. Four 

 medusa-bearing stolons arose from the four radial corners of the stomach 

 very near the points of entrance of the four radial canals. Each of these 

 stolons gave rise to from two to six medusa-buds in various stages of devel- 

 opment. When about to be set free the young medusa possesses four simple 

 tentacles and radial canals, as in the adult ; but its proboscis shows no 

 trace of the proliferating stolons. The ex-umbrella of the young medusa 

 is sprinkled over with nematocyst cells. The entoderm of the proboscis and 

 stolons is ochre-yellow, all other parts being colorless. A single specimen 



