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 Euchaeta 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 Tomopteris 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 balea, besides appendicularians (Ovkopleura dioica), Tomo- 
pteris 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 zodplankton 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, 7. gravida, 
and 17. nordenskioldi, with occasional specimens of Chaetoceras deci- 
piens, C. densum, C. atlanticum, C. contortum, Biddulphia aurita, 
