498 MEDUSAE OF THE WORLD. 



movement occurs in pronounced decrease in the intensity of light. Relative intensity in the 

 field, not ray-direction, determines the place of rest. Light is necessary for the up-swimming 

 activity, though not for directive — this being due to gravity. Contact of the bell with air and 

 the accompanying recoil probably cause the inhibition that precedes inversion of the bell at 

 the surface. 



This paper should be read in connection with those of Yerkes and Ayers, 1903, in American 

 Journal of Physiol., vol. 9, and of Morse, 1907, in American Naturalist, vol. 41. 



.Ssginopsis laurentii (see page 472) . 

 JEginopsis laurentii, Bigelow, H. B., 1909, Proc. National Museum, Washington, vol. 37, p. 314, plate 32, figs. 2-6. 



Bigelow records the capture of 46 specimens of this little-known medusa by Bryant from 

 off the coasts of Labrador and Newfoundland during the summer of 1908. The largest is 13 

 mm. in diameter. There are 4 tentacles and 8 peronial strands The 16 gastric pockets of the 

 adult are derived by subdivision from 8 primary pockets. There is no peripheral canal system. 

 There are 16 to 26 lithocyst-clubs each with 1 to 3 large concretions. No otoporpae. Gonads 

 in the ectoderm of the subumbrella wall of the 16 gastric pockets. 



Bigelow's description, accompanied as it is by clear photographs of the medusa, is the 

 best extant. 



