Naked- Eyed Medusae or Jelly Fishes. 89 



what into the gelatinous disk. In the inner cavity there are 

 four vertical muscular bundles ranging between the chymi- 

 ferous tubes, which terminate midway between the sensitive 

 bulbs ; and also eight others much smaller, alternating by 

 twos with these four. This same cavity has a transverfse 

 layer of contractile cells lining the whole interior, as was 

 distinctly observed on close examination. It properly con- 

 sists of four parts, extending from one chymiferous tube to 

 another. There is still another muscular system extending 

 between the four sensitive bulbs, within the lower margin, 

 which is made up of a thick layer of muscular fibres, with 

 which alternate some few radiating fibres crossing the former 

 at right angles, and most numerous about the eye-specks. 



It is. now well known that these Medusae, in one stage of 

 their existence, have a polyp form, and those Hydroid polyps 

 are, therefore, only imperfect Medusae. The Sarsia, in one 

 of its conditions, is a Coryna, and the species of Coryna per- 

 taining to the Sarsia mirabilis (although not figured in this 

 memoir, which treats only of these animals in their perfect 

 state of development), is well known in the Boston harbour, 

 and has been often collected by Professor Agassiz. The 

 polyp of the Hippocrene is still unknown ; but we have here 

 the suggestion, with some good reasons for admitting its 

 correctness, that it is a Tubularia, a fine species of which is 

 well known in the same harbour. 



Many other points are detailed in this memoir which we 

 have to pass by at this time. 



Besides the species mentioned as described in this paper, 

 the author briefly mentions two new species Thaumantias 

 (T. diaphana and T. pilosella) ; and also a new genus near 

 Hippocrene which he calls Nemopsis, in allusion to the fact, 

 that two of the eye-specks of each cluster have a slender 

 pedicel, instead of being sessile like the others, near the 

 bases of the tentacles. The species was taken in Nantucket 

 Harbour, June 1849, and is named N. Bachei. — American 

 Journal of Science and Art, vol. x.. No. 29, 2d Series, p. 272. 



