134 bulletin: museum of comparative zoology. 



20 net brought in very little indeed; but the coarser nets yielded 

 great numbers of the common cosmopolitan ctenophore Pleurobrachia 

 pileus, which had been previously represented only by occasional indi- 

 viduals; thus showing that we had run out of the diatom swarm. 

 And a pure diatom plankton was not met again on the run from 

 the Kennebec to Cape Ann. A haul sixteen miles S. S. W. from 

 Seguin yielded a rather barren plankton, chiefly Ceratium, with a 

 very few Asterionella but no Chaetoceras; and, as noted above, the 

 same type was found at Stations 41, and 42, which, with the data of 

 stations made in July shows that a rather sparse Ceratium plankton 

 is the normal summer type for a belt reaching from Cape Elizabeth to 

 Cape Ann, just as it is for Massachusetts Bay. 



There was a striking difference between the plankton in Casco Baj^ 

 and in Penobscot Bay. In the latter, at our only Station (21a) the 

 water was extremely barren, there being almost no microplankton, 

 except a few Chaetoceras. In Casco Bay (Station 16, 17, 20) on the 

 other hand, there was an extremely rich diatom plankton, consisting 

 almost altogether of various species of Chaetoceras and Rhizosolenia 

 with various metazoan larvae. 



At Orr's Island, on July 28, the surface water was full of Chaeto- 

 ceras and a large number of the diatom Navicula; but two days later, 

 this type of plankton had entirely disappeared, its place being taken 

 by hosts of ophiuran plutei, copepods, and small Medusae, e. g. 

 Phialidium and Sarsia, without any apparent change in the physical 

 nature of the water. 



