PLATE XXX. 



Medusina costata (p. 49). 



Fig. 1. Copy of a figure by Nathorst showing an impression of the under side of this species. The 

 mouth (m) is clearly defined, and also the impressions of the 4 genital hollows (g, g, g, g), 

 and the radiating impression between the latter and the outer margin. 



AURELIA FLAVIDULA (p. 5). 



Fig. 2. Photograph of a east in plaster of a portion of a large individual. The cast, which was 

 entire, has been cut away from the side so as to expose the impression of the lower surface 

 of the medusa. The cast of the quadrate mouth, the exterior of the genital sacs and the 

 filling of the interior of three of those sacs, portions of the four arms, and the faint 

 impression made by the radial tubes are beautifully shown. 



Fig. 3. Photograph of the cast of a large individual in which the genital sacs are shown on the 



right by an impression of their exterior and on the left by the cast of the distended interior 



cavity. The form of the quadrate mouth is clearly shown, and also the cast of the tube 



that led from the mouth to the genital sac. 



A comparison of the fossil impression, fig. 1, with the casts of the recent medusae, figs. 2 



and 3, is siiggested. 



164 



