434 bulletin: museum of comparative zoology. 



other warm water holoplanktonic Medusae or Siphonophorae, may be 

 expected anywhere within the isotherms of 20°, except in coastal 

 waters of low salinity. 



Off our coasts, north of Chesapeake Ba\', the continental slope, 

 i. e., the line of demarcation between Atlantic and coastal water, is 

 roughly the normal western limit to all these holoplanktonic species, 

 though they may sporadically reach the coast. In the coast water 

 the place of the holoplanktonic INIedusae is taken by a host of neritic 

 species. But only one siphonophore, Stephanomia cara, is anything 

 but accidental there between Chesapeake Bay and Nova Scotia ; and 

 even that one species is irregular and sporadic in its occurrence. 

 Probably for siphonophores as a whole the low salinity of the coast 

 water is an effective barrier (1911b). 



The holoplanktonic coelenterate fauna proved to be as uniform 

 quantitatively throughout the area traversed by the Bache (except for 

 the cold coast water), as it is over the tropical oceans as a whole, 

 there being no such contrast between the ocean currents and the more 

 stagnant neighboring water as obtains for the eastern Pacific (Bigelow, 

 1909a, 1911b). Thus Rhopalonema, Bougain\illea, Diphyopsis 

 bojani, Ceratocymba, and Ahylopsis tetragona, were taken at two thirds 

 or more of the thirty-three tow-net stations, while Hippopodius, 

 Diphyopsis dispar, and Diphyes appendiculata occurred at nearly every 

 station. 



There are no cosmopolitan surface Medusae in the Bache list: 

 but two examples of this habit are afforded by the siphonophores 

 Galeolaria australis and Vogtia pentacanlha; possibly a third, if 

 Diphyes fowleri proves to be a synonym of D. trumnta (p. 422). 



Considering the number of comparatively deep tow-net hauls made 

 by the Bache surprisingly few deep-sea coeienterates were captured ; 

 only one young Periphylla (p. 401) and a small series of Chuniphyes 

 vmUideniata (p. 425). Both of these have already been recorded from 

 the Atlantic (Bigelow, 1911b; Broch. 1913), the former on many 

 occasions. 



Stragglers from the north are represented by Aglantha digitate, the 

 occurrence of which in the coast water off Chesapeake Bay deserves 

 note, because this is the most southerly record of this species in the 

 Atlantic (Maas, 1906b; Mayer, 1910; ' Bigelow, 1917b). 



