324 bulletin: museum of comparative zoology. 



hauls having probably been caught in the passage of the net down and 

 up. The salinity in which it was Hving ranges from 32.1%o (Station 

 10081) to 33.48%o (Station 10073), the optimum, as shown by greatest 

 abundance, being 32.2%o to 33%o. The upper limit of temperature 

 was 76° (Station 10080), its lower limit was probably about 60° 

 (the five fathom reading at Station 10069). Thus it was living in 

 warm water; but not in salt Gulf Stream water on the one hand, nor 

 where the salinity is lowered below 32%o by the influence of the Chesa- 

 peake, on the other. And this agrees with its known occurrence, for, 

 according to Mayer (1912, p. 34) it is a creature of the pure sea water 

 along the outer shores, its place being taken by another species, M. 

 gardeni, in the brackish bays. 



The swarms of Mnemiopsis and of Pleurobrachia were mutually 

 exclusive, for though both were often taken at the same station, 

 Mnemiopsis was invariably limited to the surface waters which it 

 shared with the various Salpae (p. 269), Pleurobrachia to the deeper 

 layers. Pleurobrachia and Mnemiopsis were not found side by side 

 on the surface. 



The oceanic, like the neritic coelenterates of our waters, fall into two 

 more or less overlapping groups, according as they are at home in 

 high or in low temperatures (Fig. 81). The most typical member of 

 the former found in our coastal waters is Aglantha digitalc. The cap- 

 tures are so scattered, and from waters of such different salinities and 

 temperatures that they throw very little light on the conditions which 

 are the optimum for the genus. But it is significant that although 

 Aglantha was as abundant off Barnegat as on German Bank, only one 

 fragmentary specimen was taken anywhere within the immediate 

 influence of the Gulf Stream. And I may further point out that 

 though it is a constant inhabitant of the Gulf of Maine, it never seems 

 to attain the faunal prominence there, or anywhere further south, 

 that it does off the coasts of Newfoundland and Labrador, or in Green- 

 land waters. It is a creature of cold water, limited in its southern 

 extension by the Gulf Stream. 



The southern oceanic members of the list are Niobia dendrotentacula 

 (put in this group by its asexual multiplication), Aglaura hemistoma, 

 Rhopalonema velatum, Geryonia, Cunodantha odonaria and the sipho- 

 nophores Abylopsis, Diphyes, Galeolaria, Agalma okeni, Physophora, 

 Rhizophysa, and Physalia. The largest catch of these species was 

 in the edge of the Gulf Stream (Station 10071) where no less than eight 

 of them were taken; and four were taken at Station 10074. One or 

 other of them was likewise taken at Stations 10064, 10070, 10076. 



