320 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
ware Bay (Station 10073), its range being slightly more extensive than _ 
that of Mnemiopsis lerdyi (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% 9 (Station 10077) to about 34% 
(Station 10076), the temperature from about 65° to about 77°. 
The boreal neritic species are Melicertum campanula, Stawrophora 
mertensit, Mitrocoma cruciata, Tiaropsis diademata, Phialidium lan- 
guidum, and the northern form of Cyanea capillata. 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, 1918a, 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. 111) 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). 
