422 BULLETIN OF THE BUREAU OF FISHERIES 



Chaetoceras. The lists given below for station 20093 off the Isles of Shoals (p. 425) 

 and station 20095 off Cape Elizabeth (p. 425) may serve as representative. 



The two genera, Thalassiosira and Chaetoceras, similarly dominated the plankton 

 in the Isles of Shoals region during the April flowerings of the year 1913, as well as 

 in Massachusetts Bay, where the tow on the 3d was chiefly Thalassiosira norden- 

 slcioldi and Th. gravida, with a scattering of Chsetoceras decipiens, Ch. densum, Ch. 

 atlanticum, Ch. contortum, Biddulphia aurita, Coscinosira polychorda, Thalassiothrix 

 nitschioides, and Rhizosolenia semispina (Bigelow, 1914a, p. 405). 



Much the same lists of species — chiefly Thalassiosira and Chsetoceras — are respon- 

 sible for the April flowerings of diatoms off western Nova Scotia, in the eastern side of 

 the gulf, and out from Cape Sable across Browns Bank to the Eastern Channel (see lists 

 for stations 20103, 20105, 20106, and 20107, pp. 428, 429. But whereas Thalassiosira 

 is, on the whole, the dominant genus in the western side of the gulf in April and some- 

 times almost monopolizes the water there (p. 452), it has been entirely overshadowed 

 by a great abundance of Cluetoceras in all the hauls in the eastern side. This was 

 also the case with the rich gathering of diatoms made off the southeast slope of 

 Georges Bank on April 16 (station 20109; see list, p. 430). Douthart's tows in 

 1913 over the northern part of Georges Bank suggest that Chsetoceras is also the most 

 characteristic spring flowering diatom there (hence over the offshore banks as a whole), 

 for on April 14 Chsetoceras densum, Ch,. atlanticum, and Ch. decipiens dominated on 

 the central part of the bank, with smaller amounts of Thalassiosira nordenskioldi 

 and Th. gravida, besides a scattering of Ditylium brightwellii, Rhizosolenia obtusa, 

 Rh. styliformis, Rh. semispina, Thalassiothrix nitschioides, Asterionella japonica, 

 Coscinodiscus, Coscinosira, and the neritic genus Pleurosigma. The fact that Rhizo- 

 solenia styliformis instead of Chaetoceras dominated an equally productive gathering 

 a few miles to the westward two weeks later illustrates the local fluctuations in the 

 flowerings of different diatoms (Bigelow, 1914a, p. 415). 



As the flowerings of diatoms expand eastward along the coast of Maine and 

 offshore over the western half of the basin from April to May (p. 385) , Thalassiosira 

 continues to dominate in the coastwise belt (the seasonal expansions and contractions 

 in the range of Thalassiosira are described below, p. 449) , and Chsetoceras offshore. 

 The very rich gathering in the western side of the basin on May 5, 1915 (station 

 10267), consisting chiefly of three species of the latter, was one of the most monot- 

 onous we have made (see list, p. 429). The rich diatom plankton on the south- 

 western part of Georges Bank on May 17, 1920 (station 20128), was chiefly 

 Chsetoceras sociale (p. 430). 



The status of the diatoms in summer, autumn, and early winter is discussed 

 above (p. 391) and in the accounts of the several genera. The phenomena chiefly 

 deserving attention are flowerings of Guinardia, Thalassiothrix, and Rhizosolenia 

 on Georges Bank in July (p. 391), of Rhizosolenia in the shoalw ater off Marthas 

 Vineyard in August (p. 431), the very productive flowering of Asterionella japonica 

 along the coast of northern Maine in August, 1912 (p. 431), the persistence of an 

 abundance of Thalassiosira and Chastoceras in the region of Mount Desert Island 

 until into autumn (p. 426) and in the eastern side of the basin until late in the summer 

 of 1912 (p. 392), and the flowerings of Skeletonema and Rhizosolenia alata in Massa- 



