430 bulletin: museum of comparative zoology. 



have established the rarity of neritic Medusae in the high seas as a 

 general rule (Maas, 1893). But the fact that it is as true of the 

 region west and southwest of Bermuda as of the central Atlantic or 

 Pacific, contrasted with the rich neritic fauna of the Bahamas (Mayer, 

 1904), the straits of Florida (Mayer, 1900, Vanhoffen, 1913), and even 

 of Bermuda, has a special interest because of the close proximity of 

 the Antilles and Florida currents. These, or the product of them com- 

 bined, annually transport, perhaps are constantly transporting, many 

 of the West Indian Medusae northward for long distances. And 

 though the extreme northern limit to this migration is unknown, 

 forms which certainly began their journey as far south as Florida, have 

 often been taken in the inner edge of the Gulf Stream off Cape Cod. 

 But since the Bache records do not reveal any tendency toward dis- 

 persal seaward from the land, this migration is apparently confined to 

 a fairly definite track close to the continental slope, at least in winter, 

 which corresponds to the absence of any dominant surface drift either 

 from the continental shelf toward Bermuda, or vice versa. But the fact 

 that the neritic Medusae of Bermuda, are, as a whole, practically an 

 impoverished Bahaman fauna, including such unmistakably x\nierican 

 species as Halitiara fonnosa, Eirene pyramidalis, and Aequorca flori- 

 dmnis, is evidence of occasional transfers from the coast eastward 

 across the intervening ocean. Whether^ however, this process is 

 going on sporadically today, is by no means certain, for similarity of 

 neritic Medusae does not necessarily mean a present interchange, as 

 witness the conditions on the two sides of Central America (1909a). 



The Bache list includes two species of Anthomedusae made practi- 

 cally holoplanktonic by a budding phase, ?'. e., Cytaeis tetrastyla and 

 Bougainvillea niobe. 



Cytaeis is now known to occur very generally, although irregularly, 

 over all warm waters, Mediterranean, Atlantic, Pacific, and Indian 

 (1909a; Vanhoffen, 1911, 1912a), a distribution indicating that the 

 intervals between successive hydroid stages are sufficiently prolonged, 

 by the medium of one or more budding phases, to allow unlimited 

 dispersal in the waters suited to it by temperature. But though 

 Cytaeis is thus enabled to surmount the barrier which the ocean basins 

 impose to the dispersal of neritic Medusae, it has not attained the 

 uniformity of distribution characteristic of such truly holoplanktonic 

 coelente rates as Rhopalonema xelaium, Liriope tetraphylla, or Diphyes 

 appendicvlala. 



Bougainmllca niobe, previously known only from the Bahamas 

 (Mayer, 1900, 1904, 1910) and from one station in the south Atlantic 



