BIGELOW: COAST WATER EXPLORATION OF 1913. 305 
were sent to the greater depths did not capture many specimens in their 
passage upward through the water, is good evidence that the large 
catches were made at about the depth at which the nets were working 
horizontally. This was fifteen fathoms at Station 10104; twenty-five 
fathoms at Station 10093 and 30-35 fathoms at Stations 10092, 10097 
and10100. Thelargest catch of all was made at twenty fathoms (Sta- 
tion 10091); and the depths of the rich hauls south of Cape Cod (Sta- 
tions 10060, 10061, 10065) were twenty to forty fathoms. Limacina 
balea covers a considerable range both of salinity and of temperature: 
but was never found in the warm salt Gulf Stream water, nor is it at 
home anywhere in tropical seas. According to Meisenheimer (1906), 
it is the only pteropod endemic in the northern boreal region; and 
is a good index of boreal waters. All the captures were from salinities 
of 31.8%p or more, and the absolute maximum may have been higher 
than 35%po (Station 10064). But the few specimens from that Station 
were probably only stragglers from the coast waters. The maximum 
salinity for the rich hauls was 32.5%9-33.2% . At the two Stations 
(10091 and 10104) in the Gulf where swarms were encountered, the 
salinities were respectively 32.5-32.6%po and 31.9-32.5%o. Thus in 
summer the optimum for Jamacina balea is neither the freshest coast 
| water, with salinities of 32%po or less, nor the ocean water outside the 
| continental slope with salinity above 33%po, but the transition water. 
The temperature can be precisely stated for only four captures, 
\4. e., 55° (Station 10059), 55° (Station 10097, surface), about 48° 
| Station 10095); and 61° at Station 10103 (surface). But the fact 
| that no specimens were taken at the surface at any of the stations south 
}or west of Cape Cod indicates that none of the captures were from 
| temperatures above 60° except possibly in one or two instances; and 
jeven then (Stations 10064, 10065) the specimens may have been living 
jin much colder water. The rarity of Limacina on the surface in the 
/Gulf of Maine further simplifies the problem, because, to assume that 
ithe specimens came from even as small a depth as five fathoms, lowers 
‘the upper limit of temperature for most of the captures to about 58°. 
On the other hand, most of the Gulf specimens were certainly from 
water warmer than 46° (Stations 10091, 10095-10104); and we have 
'n0 proof that any of them were living in water colder than this, for 
pioueh the deep water temperature was 43° at several stations, there 
Sno reason to suppose that the specimens of Limacina came from the 
ie layers (p. 304). The other northern pteropod, Clione limacina, 
S-er 
vas restricted to the Gulf of Maine, where it was decidedly rare. 
-\nd we have never found it common in the Gulf, although specimens 
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