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PROCEEDINGS OF THE [April, 1857. 



mens, perhaps normally, and (I believe) in any specimen in cer- 

 tain conditions of declining activity, there exists a greater or less 

 constriction below the summit of the disk, giving the appearance 

 of a considerable emargination of the usual convex outline on 

 each side (PI. 11, fig. 2.) The disk is rather thick just above the di- 

 gestive cavity, diminishing rapidly as it approaches the bell 

 margin, which though seemingly an inconsiderable character, ne- 

 vertheless imparts a certain peculiarity not long unobserved when 

 comparing active specimens of the species with other Eucopidae 

 not similarly characterized. I have not observed any specific char- 

 acter in the form of the digestive cavity and oral appendages. 

 The sexual organs are less pyriform and more cylindrical than 

 those of Eucope thaumantioides, and in fully developed specimens 

 are so long that when the disk is somewhat contracted they fre- 

 quently appear to occupy nearly the whole distance from the 

 digestive trunk to the margin, but on the whole approaching nearer 

 the latter than the former. The bulbs of the tentacula (which 

 vary from sixteen to twenty in number,) are large and somewhat 

 conical; the lashes are contractile, but not to such a degree as to 

 disappear, only gathering themselves up into small knots on the 

 free extremity of the bulbs. I have never been able to set any 

 limit approaching exactness to their power of elongation, but a 

 specimen of the size represented in fig. 1, will sometimes drag a 

 length of tentaculum after it not much less than six inches. The 

 marginal capsules never exceed eight in number, except in cases 

 of deformity. They usually contain each five or six corpuscles 

 arranged in an arc of a circle. 



The digestive trunk is of a general yellowish tint with a red 

 nucleus. The sexual organs are uniformly yellow, and the tenta- 

 cular bulbs have each a red nucleus to the bulb, while the lash has 

 the whitish, almost frosted appearance, imparted by the presence of 

 great numbers of thread-cells. The marginal cord also is of a 

 light yellow color, whenever it enlarges to form a ganglion-like body 

 for the tentacula, but this coloration is scarcely observable for 

 those enlargements corresponding to the small marginal tubercles. 



The graceful motions of this Medusa consist of a rapid succes- 

 sion of strokes,* by which the animal is impelled with considera- 



* As a general rule, we may say (according to my observation,) that the rapidity 

 of succession of the rythmical strokes of the disk is in inverse ratio to the depth 

 of the bell. Thus taking a deep-belled and a shallow-belled species, each in full 

 activity and of nearly the same size, the latter will require a greater number of 



