320 bulletin: museum of comparative zoology. 



ware Bay (Station 10073), its range being slightly more extensive than 

 that of Mnemiopsis leidyi (p. 322). Probably it was the Chesapeake 

 current which carried it to the outer edge of the shelf off Chesapeake 

 Bay. Aequorea groenlandica like Mnemiopsis was living chiefly at 

 the surface and for a fathom or so down, the deeper hauls yielding very 

 few even where many were seen floating past the ship. The range of 

 salinity was from about 31.3%o (Station 10077) to about 34%o 

 (Station 10076), the temperature from about 65° to about 77°. 



The boreal neritic species are Melicertum campanula, Staurophora 

 mertensii, Mitrocoma cruciata, Tiaropsis diademata, Phialidium lan- 

 guiduni, and the northern form of Cyanea capiUata. In July and 

 August these are all confined to the waters east and north of Cape Cod, 

 (Fig. 79) though they appear in winter in the sounds and bays, as far 

 west as Narragansett Bay. The occurrence of Phialidium, and Stauro- 

 phora has been commented on (p. 274), and I need merely add that the 

 rarity of the others in the central part of the Gulf agrees with our 

 experience in 1912 (1914a). 



Two important species, Mnemiopsis leidyi and Pleurobrachia pileus 

 are intermediate between neritic and oceanic, for though neither has a 

 fixed stage, and though Pleurobrachia occasionally occurs far from 

 land, it is distinctly a creature of coast waters rather than of the open 

 ocean (Kramp, 1913a, p. 532), while this is even more true of Mnemiop- 

 sis. The range of Pleurobrachia extends unbroken from Labrador 

 (1909c) at least as far south as Pamlico Sound (1913a, p. Ill) and per^ 

 haps farther. And we found it more generally distributed in the coast 

 waters than any other coelenterate, swarming locally south as well as 

 north of Cape Cod (Fig. 80). 



From the distributional standpoint, localities where a species does 

 not occur may be fully as significant as those where it does. And this 

 is particularly true of Pleurobrachia, for it was absent in the inner 

 edge of the Gulf Stream (Stations 10061, 10064, 10071, 10076, in the 

 shoreward tongue of the Gulf Stream off Delaware Bay (Station 10073), 

 on the one hand, and in the fresh water at the mouth of Chesapeake 

 Bay (Station 10078) on the other. Otherwise there were only two 

 Stations over the shelf where we failed to capture it (10081, 10083), 

 at one of which (10083) the nets yielded very little of anything (p. 272). 

 Pleurobrachia was taken at exactly half the stations in the Gulf of 

 Maine, a rather larger proportion of occurrences than in 1912 (1914a, 

 p. 126). But the species was rather more restricted in its range in the 

 Gulf than in that year, occurring only once (Station 10103) in the 

 coastal zone between Cape Ann and Penobscot Bay; and not at all 

 in the central part of the Gulf (Stations 10090, 10092, 10093). 



