BIGELOW: COAST WATER EXPLORATION OF 1913. oLo 
_ The extreme range of salinity for Pleurobrachia was from about 
, 31.6% (surface, Station 10066) to about 35% (fifteen fathoms, 
(Station 10074). But most of the captures were from water of about 
32%0-33.4%o. And there is only one Station where it is safe to assert 
that Pleurobrachia was living in water salter than 34%p, 7. e., at Station 
10074, where the number taken in the horizontal haul at fifteen fath- 
oms was so large that most of them must have been captured at about 
that depth, not in the short column of water through which the net 
fished on its way down and up (there were none on the surface). 
The major part of the haul at Station 10077 was likewise in water of 
about 34.5% 0; but so few specimens were taken that they may have 
come from anywhere between the surface and the greatest depth 
reached by the net; 2. e., from a salinity anywhere between 31, .4%o 
and 35% o. ‘The southern swarm was living in water of about 32% 
to 33.2% ; the northern one (German Bank) in 32.8% to 32.9%o. 
~ Rose (1913) has recently shown that the density of the water 
‘influences the vertical movements of Pleurobrachia; it is therefore 
worth while to correlate this physical constant with records for the 
genus. Near New York, where the captures can be located within a 
few fathoms because of the shallow water, they were from densities — 
| ranging from 1.022 (Station 10066, surface) to upwards of 1.0237. 
| And the specimens taken at Stations 10082 and 10074 probably were 
living at a density of about 1.0252 to 1.0254. But the German 
| Bank specimens were in much heavier water (nearly 1.026). Thus 
there does not seem to be any connection between the occurrence of 
Pleurobrachia, and density within a range of 1.022 to 1.026. But it is 
noteworthy that we found none in water lighter than 1.022, and sel- 
| dom in densities less than 1.023, while it is doubtful whether any speci- 
| mens were living in the densities of 1.027 and over, which characterize 
. the bottom water of the deeper parts of the Gulf of Maine. 
. Mnemiopsis leidyi was generally distributed over the inner half of 
| the continental shelf between Barnegat and Delaware Bay; and the 
}mid-zone of the shelf south of the latter (Fig. 80). None were seen 
north of Barnegat though the species is abundant in the bays and 
sounds of the southern coast of New England later in the season, or 
joff Chesapeake Bay. But the latter is not its southern limit, though 
it may interrupt the continuity of its range. It was most abundant 
near the coast, from Barnegat to Cape May, and again between 
Stations 10074 and 10075, swarming on the surface in myriads, and 
ausing brilliant phosphorescence at night. And it seems to have 
been limited to a very shallow surface zone, the few taken in the deep 
. 0 
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