[7] 



MEDUSA FROM THE GULF STREAM. 



933 



prominent by the bases of attachment being left in intaglio by the nius- 

 cnlar regions which separate them. They follow the same radial conrse 

 as the exumbral depressions in the marginal lappets above, and seem to 

 indicate the i)oints of fnsion of the npper and lower umbral walls. The 

 exumbral furrows mark the lines of attachment of ends of the muscles, 

 which onthe subumbral side are connected by a narrow zone formed of 

 sixteen muscular swellings homologous with the coronal muscle of the sub- 

 umbrella of Atolla, where, however, instead of being broken or externally 

 depressed at its attachments, the muscle is continuous, at least in Verrillii 

 and Bairdii. In Periphylla there are sixteen subumbral radial muscles 

 separated by as many radial furrows. A radius, therefore, which i)asses 

 through a tentacular base or the style of a marginal sense-body bisects 

 one of these muscles, which together form the coronal subumbral zone. 

 On the inner boundary of this zone begins the region of the proboscis 

 or stomach, which occupies the whole central part of the subumbrella. 

 The arrangement of the parts which form the stomach walls could be 

 well studied in two specimens in which the upper surface of the bell was 

 more or less infolded, and the coronal i)art brought to the level of the 

 apex of the bell, while the stomach walls are stiffly protruded. The 

 stomach or proboscis has the form of a sac which is made up of plates 

 of different sizes united together. From a point cut by the radius pass- 

 ing through the middle member of the three tentacles which alternate 

 with the four sense-bodies, two-thirds the distance between the center 

 and bell margin, a thickened support for the stomach walls is found. 

 This support spreads out into a flat plate, which, becoming broader, 

 unites with a similar support from the next quadrant, and in that way 

 the comi>leted stomach wall is formed. The portion of the stomach 

 wall adjacent to the lips of the mouth has the same color in the alco- 

 holic specimens as the marginal lappets. The lips are destitute of mar- 

 ginal tentacles, although the rows of gastral filaments can be seen on 

 the inner stomach walls, and one or two protrude outside the mouth. 



Periphylla hyacinthina, Steenstrup. 



specimens examined. 



