86 EUCOPE POLYGENA. 



Eucope alternata A. AGASS. 



Eucope diapJiana AGASS. (ex. p.). Cont. Nat. Hist. U. S., IV. pp. 322, 352, PI. 34, Figs. 1-9. 

 1862. Non Th. diaphana AGASS., Meru. Am. Ac. 



This species was at first mistaken by Professor Agassiz for the young 

 of Thaumantias diaphana^ figured in the Memoirs of the American 

 Academy. The development of the Hydrarium of these two closely 

 allied forms shows that two species have been confounded. 



Massachusetts Bay, Nahant (Agassiz). 



Cat. No. 83, Nahant, Mass., Aug. 1861, A. Agassiz. Hydromednsarimn. 



Cat. No. 84, Nahant, September, 1854, H. J. Clark. Hydrarium. 



Cat. No. 85, Nahant, May, 1862, A. Agassiz. Hydrarium. 



Cat. No. 86, Nahant, July, 1861, A. Agassiz. Hydrarium. 



Cat. No. 87, Nantasket, April, 1861, H. B. Rice. Hydrarium. 



Cat. No. 88, Nahant, L. Agassiz. 



Cat. No. 394, Nahant, July, 1862, A. Agassiz. Hydromedusarium. 



Cat. No. 395, Nahant, June, 1862, A. Agassiz. Hydromedusarium. 



Eucope polygena A. AGASS. 



The only adult Medusa of the genus Eucope, of which we know 

 the complete development, being Eucope diaphana, it is not possible 

 at present to decide whether we have not among these closely allied 

 Campanularians the Hydraria of several genera. There are certainly 

 differences among the young Medusae, at the moment of escaping 

 from the calycles, which must give them totally distinct characters 

 when adult, to judge by what we know of the mode of development 

 of marginal tentacles, and the increase in size of the genital organs. 

 There is a great similarity in the young Medusaa of Eucope articulate^ 

 E. pyriformis, E. alternata, and E. polygma, all these species having 

 twenty-four hollow tentacles, and ovaries close to the base of the pro- 

 boscis, at the time they escape from the reproductive calycles ; while 

 in E. diaphana and E. geniculata Gosse we have twenty-four tentacles, 

 nearly solid, and no ovaries in the younger stages. Another type 

 occurs in Obelia commissuralis and Laomedea gelatinosa of English 

 authors, where the Medusa has sixteen tentacles and no ovaries ; 

 and finally there is a still different type in the Eucope fusiformis 

 and Laomedea divaricata of McCrady, in which we find forty-eight 

 tentacles at the time of hatching, and long spindle-shaped genital 

 organs along the chymiferous tubes. These are undoubtedly good 

 structural characters upon which genera can easily be distinguished, 

 but it would be premature to make all these divisions until we know, 



