86 EUCOPE POLYGENA. 



Eucope alternata A. Agass. 



Eucope diap/iana Agass. (ex. p.). Cont. Nat. Hist. U. S., IV. pp. 322, 352, PI. 34, Figs. 1 - 9. 

 1862. Non 3'A. diaphana Agass., Mem. Am. Ac. 



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

 of Thaumantias dicqjhana, figured m 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. Hydromedusarium. 



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 Eucojie 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 

 difierences among the young Meduste, 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 Medusas of Eucope arllndata, 

 E. 2)yriformis, E. alternata, and E. j^oli/gena, 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. diajj/iana and E. genicidata Gosse we have twenty-four tentacles, 

 nearly solid, and no ovaries in the younger stages. Another tA-pe 

 occurs in Obelia commissuraUs and Laomedea gelatinosa of English 

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

 and finally there is a still difterent type in the Eucope fnfiiformis 

 and Laomedea divarlcata 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 undoul^tcdly good 

 structural characters upon which genera can easily be distinguished, 

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



