﻿160 



PROCEEDINGS OF THE 



[April, 1857. 



crene, but " differs from it in having a more movable and bottle- 

 shaped digestive cavity, which may be more or less protruded 

 from the main cavity of the body, and is not so persistent in its 

 form as that of Hippocrene. The tentacles are arranged, as in 

 Hippocrene, in four bunches, with eye-specks at their base; but 

 there are two of these eye-specks, supported upon two distinct 

 stalks, rising above the others and above the tentacles, similar in 

 appearance to the protruding eyes of a snail. " 



I have had frequent opportunity of examining this genus, and 

 have particularly sought for an ocellus at the enlarged extremi- 

 ties of these tentacula, but I am satisfied that these bulbs in our 

 species at least, contain no pigmentary matter, their deeper hue 

 being owing to their greater thickness and their consequent ap- 

 proach to opacity. A true ocellus, however, is found at the base 

 of each of these organs precisely, as in the filiform tentacula. 

 See fig. 10/ pi. la. 



The larva of Nemopsis, (PL 10, fig. 7.) as observed by myself, 

 is a free hydroid, with a base broader than that portion of the body 

 which contains the digestive cavity. The stem is represented by 

 a solid knob in the middle of this expanded base. There are two 

 circles of tentacula, one about the expanded base, the other around 

 the mouth. That around the base is composed of two rows, the 

 tentacula of which alternate with one another. The medusa-buds 

 are developed directly from the sides, of the polyps, between the 

 two circles of tentacula, as in Tubularia. They are not disposed 

 in grape-like branches. 



The tentacula of the Medusae are developed externally, and may 

 be distinguished, apparently, before the cavity of the bell is open. 

 The sexual organs are at first confined to the walls of the digestive 

 cavity, and do not grow downwards until comparatively late in 

 the animal's life. The clavate tentacula are also absent until the 

 animal has attained considerable size. 



Distribution. — Coast of the United States, Long Island Sound, 

 and Charleston Harbor. 



NEMOPSIS GIBBESII, nov. spec. 

 PL 10, Ff. 1-7. 



This species differs considerably from Prof. Agassiz's figure, 

 loc. cit. The general form of the fully grown animal when at 

 rest, is almost spherical, the tentaculiferous margin being then 

 somewhat contracted, but when in motion it appears truncated 



