140 ■ DISCOPHOR^. Part III. " 



has described in the Memoires of the Academy of St. Petersburg under the name 

 of Cassiopea Mertensii (Pis. XXL, XXII., and XXIII), and afterwards under that of 

 Rhizostoma Mertensii, considering it, however, as a sub-genus of Rhizostoma, to 

 which he gave the name of Polyclonia. These two MedusJB belong, unquestion- 

 ably, to the same genus, and Polyclonia differs so much from the type of Rhizos- 

 toma jiroper, Rhizostoma pulmo, that I do not only consider it as a separate genus, 

 but also as the type of a distinct family among the Rhizostomeoe. That Polyclonia 

 constitutes a distinct family, is at once apparent when the ramifications of the arms 

 are considered; and a comparison of the structure and mode of combination of 

 its spheromeres still further justifies their sejjaration. 



In order to avoid repetitions, I would first point out the figures in which I 

 have represented anew the Medusa of Pallas, on my Plates XIII. and XIIP. These 

 figures differ in appearance so much from that of Pallas, drawn from specimens 

 preserved in alcohol, which had been sent to him by Dr. Drury, that it is neces- 

 sary I should here insist upon the identity of the Medusa I have represented 

 under the name of Polyclonia frondosa, and the Medusa frondosa of Pallas. His 

 description, in the first place, agrees with the specimens I have seen ; secondly, my 

 specimens were obtained in the same jiart of the ocean from which he obtained 

 his ; and, finally, specimens which I preserved myself in alcohol exhibit exactly the 

 appearance of that figured by Pallas. Under these circumstances there can be no 

 doubt that they all belong to one and the same sjiecies. 



This Medusa is one of the most singular Acalephs I know, both on account 

 of the different asjsects it presents in different attitudes, and on account of its 

 habits. It is quite common upon the reef of Florida; I have seen immense num- 

 bers at Key Largo and at Key West, and occasionally at other points along the 

 reef, and yet it is hardly ever seen near the surface of the water. This is owing 

 to its habit of groping in the coral mud, at the bottom of the water, where 

 thousands upon thousands may be seen crowded together, almost as closel}^ as they 

 can be packed upon the bottom, at a depth of from six to ten feet. When 

 disturbed they do not rise, but crawl about like creeping animals, now and then 

 only flapping their umbrella, like other Discophora?. That Polyclonia Mertensii has 

 similar habits, I infer from the statement of Mertens, that he observed his species, 

 in large numbers, in shady places of the lagoons of Ualan, overhung with Sonne- 

 ratios and Mangrovite. The Polyclonia frondosa is also found among the mangrove 

 islands of the Florida Reef, in shady places, near the roots of mangrove trees. 

 Mertens, however, states that he found them constantly with their arms spread and 

 turned upward, resting upon the ground; I have always seen them in the reverse 

 position, the arms downward. OtherAvise, my observations agree with those of 

 Mertens as to the mode of living of these Acalephs. 



