272 CTENOPHORiE. Part II, 



is depressed in the direction of the circumscriljcd area, and the lateral spheromeres 

 slightly project upon its sides. I infer that the possibility of protruding xniifonnly 

 the abactinal end of the body, in BCroe Forskali, may depend upon an even 

 development of the eight spheromeres on their abactinal side. If this be so, the 

 generic separation of these two animals and their allied species is fully justified. 

 There is another peculiarity which coincides Avith this diiference in form. In Idyia 

 the circumscribed area is very much elongated, and its margin adorned with a row 

 of fringes, diverging forward and Ijackward, and rounded ofl* at its anterior and 

 posterior extremities j while in Beroe proper the fringes encircling the circumscribed 

 area give it a lanceolate form. Had these characters been observed only in two 

 species, they might be considered as specific differences ; but all the conical Beroids 

 thus far figured by Mertens and Lesson agree in every respect with that so beauti- 

 fully illustrated by Milne-Edwards, as closely as those with the dome-shaped outline, 

 figured by Peron, Chamisso, and Sars, resemble that which I have examined. And 

 though the repetition of the same character in several species is not in itself a 

 generic distinction, it is generally a good indication, that such species, having closer 

 afiinities, may also present true generic peculiarities not yet observed. As I never 

 had an opportunity of examining a conical species of Beroid, it is imj^ossible for 

 me to give a more direct account of the generic differences of the members of 

 this family. I will therefore only say in conclusion, that, taking Beroe Forskali 

 as the type of Beroe proper, I would refer to it also Bei'oe mitrteformis of Lesson, 

 the type of his genus Cydalisia, and Mertens's Beroe penicillata ; and, taking the 

 species of our coast as the type of the genus Idyia, I would refer to it the oldest 

 species for which it was instituted, and Beroe cucumis of Sars, Beroe macrostomus 

 of Peron, Beroe capensis of Chamisso, and a new species discovered by my son 

 Alexander Agassiz in the Gulf of Georgia. 



For our species I propose the name of Idyia roseola. This is the species 

 alluded to in my paper on Beroid Medusa) in the Memoirs of the American Academy, 

 which, at the time of its publication, I knew too imperfectly to describe. In the 

 year 1858 it appeared in such quantities upon our coast during the whole summer, 

 that at times it would tinge with its delicate rosy hue extensive patches of the 

 surface of the sea during the warmest hours of the day. It made its first 

 appearance early in July, when all the specimens were of a small size, rarely 

 exceeding an inch or an inch and a half But it grew rapidly larger and larger, 

 and towards the end of August most of them had reached the size of from three to 

 four inches in vertical height, and aljout half that size in width, while many had 

 twice these dmiensious. At this period they were brightest and deepest in theu^ 

 coloration, the darker colored ovaries, and especially the deep pink colored spermaries, 

 adding to the intensity of their hues. But as the spawning season advanced, and 



