406 bulletin: museum of comparative zoology. 



Coscinosira polychorda, Thalassiothrix nitzschioides, and Rhizosolenia 

 semispina. 



It is interesting to note that the diatom swarm was not uniformly 

 distributed. On the contrary, while the net was towing near the 

 surface, we could see it pass through clear bands, as well as through 

 bands of diatoms, which gave it a browii color. This observation 

 shows, too, how erroneous an idea of the quantitative richness of 

 diatoms in the waters of Massachusetts Bay would have been afforded 

 by a single vertical haul with a quantitative net. 



At this same station the zooplankton w^as as poor as the diatom 

 plankton was rich, the only large organisms yielded b}^ the nets being 

 a few dozen copepods, one Euthemisto, two Clione limacina and a few 

 unrecognizable bells of some agalmid siphonophore, besides a few 

 barnacle (Balanus) nauplii, and, to my surprise, a considerable num- 

 ber of tests of Foraminifera. This was the first haul in which there 

 were no Sagittae. 



The diatom swarm continued at its height during the first half of 

 April, hauls on the 14th (St. 10,056) yielding the same rich Thalas- 

 siosira plankton just described, and the zooplankton still proved to be 

 very scanty, the catch being only a few Calanus, one Tomopteris, one 

 Sagitta elcgans, one fragmentary Beroe, and one young Staurophora. 

 But there were considerably more Balanus nauplii than before. 



No plankton hauls were made north of Cape Ann, except the one 

 station in Ipswich Bay noted above, previous to March 29th. But 

 from that date onward, Mr. Welsh's stations show that the Thalassio- 

 sira swarm filled the coast water very generally from Cape Ann to 

 Cape Porpoise during the whole of April, often being so dense as to 

 discolor the water. Thus on May 2, he writes " the water yesterday 

 and today full of green slime," and on the 3d, " the water is full of the 

 greenish brown algae." Microscopic examination of his catches 

 showed that the plankton was extremely uniform qualitatively, con- 

 sisting almost altogether of.Thalassiosira, with an occasional specimen 

 of the other species noted for Stations 10,055 and 10,056 (p. 405). 

 The catches were very clean up to about the first of May, but about 

 that date, they began to contain noticeable amounts of diatom debris, 

 and as the season progressed the relative amounts of dead specimens, 

 and variously fragmented remnants, grew progressively greater until 

 by the 25th of the month there were \'ery few living diatoms, con- 

 trasted with large amounts of debris, among which the various genera 

 which formed the swarm (particularly Chaetoceras and Thalassiosira) 

 could be distinguished. In the latest hauls there were hardly any 



