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PROCEEDINGS OF THE 



[April, 1857. 



colonies established, their multiplication becoming so great dur- 

 ring a favorable season that the rocks literally appear clothed 

 with the yellow stems and rose-colored blossom-like bodies of these 

 flower-animals. There is, however, in their coloration, as is usual 

 in these Medusa? a combination of yellow and a shade of red, which 

 are not distributed in the same proportion in different clusters of 

 individuals, so that a series of varieties are produced between an 

 almost uniform yellow where the red is reduced to a minimum, 

 and a most beautiful rosy tint which is characteristic generally of 

 the finest and most vigorous clusters. 



III. HIPPOCRENIDJE. 



General form of the Medusas always more or less spherical ; bell- 

 wall very thick, especially above the digestive trunk, in free animals. 

 Tentacula, grouped in bunches or tufts round the bell-margin; a 

 single marginal bulb thus corresponding to a plurality of tentac- 

 ula. Ocelli present in free animals, and borne sometimes on the 

 bulb, sometimes on the tentaculum. Digestive trunk short, with 

 the sexual organs disposed about it in four distinct lobes, which, 

 in one genus, afterwards acquire an unusual connection with the 

 radiate tubes; mouth with a simple or undulate border, and armed 

 with four or more cirrhi, generally more or less branched. 



The larvae of these Medusae present, at first sight, more dissimi- 

 larity to each other than those of the other groups of the same value. 

 They are Tubularia-like hydras, with sometimes two, sometimes 

 only one whorl of tentacula; the larvae are either fixed or free ; 

 the medusa-buds are developed either as in Tubularia, between 

 the two whorls of tentacula, or upon different parts of the stem. 

 Sometimes this stem is apparently altogether wanting; sometimes 

 it is a branched, tree-like structure, nearly six inches in height. 

 The free or fixed condition of the larvae is a difference of no 

 greater than generic consequence, The other difference, that in 

 the number of tentacular whorls, is probably to be explained by 

 the history of Stimpson's genus, Acaulis, which, at first, has two 

 whorls, but afterwards loses the lower, which circumstance then 

 gives the medusa-buds, growing originally, as in Tubularia, 

 between the two whorls, the appearance of being developed 

 upon a stem. It may be, however, that the same indiffer- 

 ence as to whether the medusae be developed on the stern or 

 among the tentacula, which we see in Corynidae, may be the true 

 explanation here also. Stimpson's suggestion as to the homology 



