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 

 and 10100. The largest 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 

 bcdea 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%o or more, and the absolute maximum may have been higher 

 than 35%o (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%o-33.2%o. At the two Stations 

 (10091 and 10104) in the Gulf where swarms were encountered, the 

 salinities were respectively 32.5-32. 6%o and 31.9-32 5%o. Thus in 

 summer the optimum for Limacina balea is neither the freshest coast 

 water, with salinities of 32%o or less, nor the ocean water outside the 

 continental slope with salinit}- above 33%o, but the transition water. 

 The temperature can be precisely stated for only four captures, 

 i. 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 alcove 60° except possibly in one or two instances; and 

 even then (Stations 10064, 10065) the specimens may have been living 

 in much colder water. The rarity of Limacina on the surface in the 

 Gulf of Maine further simplifies the problem, because, to assume that 

 the 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 

 no proof that any of them were living in water colder than this, for 

 though the deep water temperature was 43° at several stations, there 

 is no reason to suppose that the specimens of Limacina came from the 

 deepest layers (p. 304) . The other northern pteropod, Clione limacina, 

 was restricted to the Gulf of Maine, where it was decidedly rare. 

 And we have never found it common in the Gulf, although specimens 



