Chap. HI. GENUS IDYIA. 287 



like herrings or maclverels. Tliey feed upon other Ctenophora^, and are very voracious, 

 their digestion being very rapid. They are short-lived, and appear periodically 

 in the early part of the sninmer, when their dimensions are one sixth of their 

 full size : they are at first pale, but grow deeper and deeper in color as they 

 enlarge, and are brightest toward the end of the summer during the spawning 

 season ; after the ovaries and spermaries have been emptied, they grow paler and 

 paler; and, finally, they are broken up into fragments by the autumnal gales. The 

 young, hatched about this time, probably pass the winter, like most shore animals, 

 in deeper water ; and they differ from the adults chiefly in having their rows of 

 locomotive flappers much shorter than afterwards. They are usually found associ- 

 ated with Pleurobrachia, Bolina, and Thamnantias near the surfixce of the water 

 during the hottest hours of the day ; but Avhenever the sea is rippled or the sky 

 overcast, they sink out of sight below the surface. 



A comparison of Idyia roseola with another species, Idyia cyathina A. Ag., dis- 

 covered by my son in the Gulf of Georgia, has satisfied me that such are truly 

 the specific charactei's of oin- Idj-ia ; for I find that there is not the slightest 

 structm-al difference between the two, and yd there can be no doubt that they 

 differ specifically. In Idyia cyathina the spherosome widens rapidly from the 

 abactinal pole, and is widest at two thirds of the distance from the mouth, when it 

 again tapers suddenly, and then more gradually, in the same direction ; the actinal 

 side of the spherosome being narrower and thinner than the actinal, and therefore 

 much more flexible, and the anterior and posterior interambulacra on that account 

 capable of more extensive contractions, in consequence of which the angles of the 

 mouth may be drawn into very deep curves, and the lips thus formed assume 

 the shape of more distinct lol^es than is ever the case with Idyia roseola. It may 

 be said, that though both have the same pattern, Idjda roseola has rather the 

 form of a shuttle, and Idyia cyathina resembles more an Etruscan vase. The habits 

 of Idyia cyathina have not been sufficiently studied to carry farther the comparison 

 of the two species ; but, as mentioned above (p. 250, note), so much is already 

 known, that it is also found associated with a Pleurobrachia and a Bolina. 



Many years ago I noticed in the harbor of Charleston, South Carolina, and in 

 Florida, two Acalephs belonging to the family of the true Beroids, respecting which 

 my memoranda are very scant}', and quite insufficient to describe them as they 

 should be. And yet I am unwilling to omit them entirely, as they seem to 

 indicate the presence, along our southern coast, of a genus intermediate between 

 Pandora and Idyia, and thus far unknown. Their most striking peculiarity is the 

 shortness of the vertical axis, which l:)arely exceeds the longitudinal diameter. In 

 this respect they resemble the genus Pandora Esch. ; ))ut they differ from it in 

 having their ambulacra very prominent and the interamljulacra concave, while in 



