BIGELOW: OCEANOGRAPHY OF MASSACHUSETTS BAY. 405 



twenty specimens of Sagitta in the haul, while we encountered a 

 swarm of copepods, almost pure Calanus finmarchicus, with one C. 

 hyperboreus and one Euchnda norvegica, no less than 225 cc. being 

 taken in the net. And this tow was decidedly richer, quantitatively, 

 than any we had made since summer. Qualitatively it was extremely 

 monotonous, the only large organisms, besides copepods and Sagittae, 

 being a few Euthemisto, four Tomoptcris helgolandica, unrecognizable 

 fragments of an agalmid siphonophore, a few fish eggs, and a pycno- 

 gonid, the latter, of course, an accidental visitor from the bottom. 

 The microplankton, likewise, was decidedly richer in bulk in Ipswich 

 Bay than on the Massachusetts Bay side of Cape Ann, with fully as 

 many diatoms (Chaetoceras) as Ceratium. 



At our coldest Station (10,053, February 13th) Sagittae had usurped 

 the chief importance from the copepods, there being 125 cc. of the 

 former, and only about 50 cc. of the latter. The most abundant 

 species was S. elegans; while the copepod swarm consisted chiefly of 

 Calanus finmarchicus, as usual, with an occasional Euchaeta norvegica. 

 The tow likewise yielded a considerable number of the boreal pteropod 

 Limacina balca, besides appendicularians {Oihopleura dioica), Tomo- 

 ptcris helgolandica, and fragments of Beroe. 



Up to this time the plankton had been decidedly uniform, the most 

 important change being an irregular but unmistakable increase in the 

 relative number of Sagittae. But when the water began to grow 

 warmer, the zooplankton decreased noticeably in quantity. Thus on 

 March 4th, there were only 15 cc. of copepods (chiefly Calanus fin- 

 marchicus) in the haul, and only twelve specimens of Sagittae (S. 

 elegans), nine Tomopteris, a few Euthemisto, and very little else 

 except a considerable number of haddock eggs. On the other hand, 

 the no. 20 net haul showed that there had been an appreciable increase 

 of diatoms, chiefly Chaetoceras, with a few Coscinodiscus, and Thalas- 

 siothrix, these forms combined far outnumbering the few Ceratium 

 (C tripos and C. fusus). Later stations showed that this haul fore- 

 shadowed the vernal diatom swarm, a phenomenon now well known 

 for the North Sea and for other parts of the eastern side of the north 

 Atlantic. Thus on April 3d (Station 10,055) the water was 

 visibly cloudy, and the nets were soon clogged with a slimy brown 

 mass of diatoms. However, it was not a Chaetoceras plankton, as 

 might have been expected from our earlier work; but was almost 

 exclusively composed of two species of Thalassiosira, T. gravida, 

 and T. nordenskioldi, with occasional specimens of Chaetoceras deci- 

 piens, C. densum, C. atlanticum, C. contortum, Biddulphia aurita, 



