322 bulletin: museum of comparative zoology. 



of New York (Stations 10060, 10063, 10066). The only place where 

 Pleurobraehia was abundant in the Gulf of Maine in 1913 was German 

 Bank (Station 10095), where small specimens swarmed. The southern 

 swarm of Pleurobraehia only once reached the surface (off Scotland 

 light-ship, July 12)." Elsewhere it was limited to depths below about 

 five fathoms; the water being from 15-30 fathoms deep over its area 

 of abundance in this region. There were no Pleurobraehia in the 

 immediate surface layers where Salpae and Mnemiopsis often swarmed 

 (p. 269). And the absence of Pleurobraehia in the immediate surface 

 laj^ers and on the surface can not be credited to the effect of sunlight, 

 because this was as true of night as of day time stations. Most of the 

 Gulf of Maine captures were likewise in deep hauls; and there were 

 none on the surface on German Bank, where a rich haul of Pleuro- 

 braehia was made at twenty fathoms. 



The shallowness of the water in the region where Pleurobraehia 

 was most abundant, and the general rarity of the genus on the surface, 

 make it easy to establish the salinity and temperature in which it was 

 living. The warmest water in which we can certainly establish its 

 presence is 69° (Station 10066, surface), though some of the specimens 

 from Stations 10074, 10077, and 10079, may have come from still 

 warmer water. And south of New York in general the captures must 

 have been in water warmer than 59°, that being the lowest tem- 

 perature through which the nets fished. The swarm off New York 

 was in temperatures of 50° (ten fathoms) to 65° (surface near Scot- 

 land light-ship). East of New York Pleurobraehia was usually living 

 in water colder than 60°, with the minimum certainly as low as 48° 

 (Station 10095), probably as cold as 43° (deep hauls in the Gulf). 

 That is to say the genus covered practically the entire range of tem- 

 perature encountered during the cruise, except the very warmest. It 

 is not surprising to find Pleurobraehia at home in extremes as wide 

 apart as this, because its range is known to be practically independent 

 of temperature. Nevertheless, there is some evidence that specimens 

 of Pleurobraehia grow much larger in cold than in warm water, as 

 Esterly (1914) has pointed out for the Pleurobrachias of the west 

 coast of the United States. And our captures strengthen this view, 

 for although the genus swarmed in water warmer than 58° off New 

 York and further south, the specimens taken there were all sm.all (less 

 than 10 mm. long). It was only in the cold water of the Gulf of Maine 

 that we found large specimens; and work in previous years has shown 

 that specimens upwards of 30 mm. long are common at the mouth 

 of the Bay of Fundy, in summer, in temperatures of 50°-55°. 



