BIGELOW: MEDUSAE AND SIPHONOPHORAE. 429 



follow the continental slope northward. As is well known, the main 

 axis of this great current lies close to the slope; while the waters 

 immediately west and southwest of Bermuda, on the contrary, are 

 part of the eddy which occupies the central portions of the North 

 Atlantic (Deutsche seewarte, 1882; Schott, 1902; 1912; Soley, 

 1911). 



On oceanographic grounds the pelagic coelenterate fauna of the 

 Cape Hatteras- Bermuda-Bahamas triangle might be expected to con- 

 sist of the following elements: — 



1. Neritic Medusae, reaching the ocean basin as immigrants 

 from the Bahamas, West Indies, Gulf of Mexico, and American coast 

 on the one hand; from Bermuda, perhaps even from the eastern side 

 of the tropical Atlantic, via the equatorial drift and Antilles current, 

 on the other. 



2. The warm water holoplanktonic Medusae and Siphon ophorae, 

 which range, undifferentiated, over the entire tropical and subtropical 

 zones of all three great oceans, Atlantic, Indian, and Pacific (1909a, 

 Vanhoffen, 1902). 



3. Cosmopolitan holoplanktonic forms; {. e., those whose distribu- 

 tion is independent of temperature. 



4. Species at home, not on the surface, but in the low temperatures, 

 and dim light of the intermediate, or even abyssal, depths, most at 

 least, of which, are practically cosmopolitan over the ocean basins. 



5. Cold water forms; stragglers from the north. 



The neritic, and holoplanktonic categories, it is true, are con- 

 nected with each other by such Medusae as prolong the interval 

 between fixed (hydroid) stage and fixed stage through the medium 

 of one or more budding phases ; nor can hard and fast lines be drawn 

 between any of the groups. But they afford a convenient working 

 classification. 



The Bache collection contains the following typically neritic 

 Medusae; Stomotoca j^terophylla, Pandea conica, Laodicea cruciata, 

 Aequorea aequorea, Nausithoe punctata, while Chanjhdea marsupialis 

 var. xaymachana, C. alaia, Linuche unguiculata, Calycopsis papillata 

 and Eutiara mayeri probably belong here also. But most of these 

 were taken at only one or two stations each, either in the Gulf Stream 

 close to the Continental Slope (Station 10,161), in the Straits of 

 Florida, or off the Bahama Bank within the sweep of the Antilles 

 current (Station 10,211). And only twice were neritic Medusae taken 

 far from land, a Pandea conica at Station 10,171, a Charydea marsupia- 

 lis at Station 10,188. The records of previous deep-sea expeditions 



