324 bulletin: museum of comparative zoology. 



10261), and in the coastal waters off Marthas Vineyard (Stations 

 1025S-10260). But it has not been detected in the tow over the slope 

 south of Cape Sable (Station 10233), or an\'^-here on Georges Bank, 

 in the Gulf of Maine, or on the continental shelf south of Nova Scotia, 

 which supports the thesis that it is distinctively a warm water species 

 off this coast. 



Though no quantitative hauls were made for microplankton, the 

 horizontal hauls give a rough index to its abundance, when this \-aries 

 as greatly, from place to place, as it does in our coastal waters in 

 summer. Microplankton was very scanty indeed along the southern 

 edge of the continental shelf, over the slope, in the southeast corner of 

 the Gulf of Maine, (Station 10225); the Eastern Channel, and on 

 Brown's Bank (Stations 10227, 10228). The Nova Scotian waters 

 (Stations 10229-10237) were, if possible, even more barren, a half- 

 hour's haul usually \ielding a mere trace. On the other hand the 

 hauls off Lurcher Shoal (Station 10245); off Mt. Desert (10248); off 

 Penobscot Bay (10250); off Cape Ann (10253) and near Marthas 

 Vineyard (10258) were very productive; for example, the volume of 

 the catch of the no. 20 net, 24 ccm. in diameter, towing one half hour, 

 was 40 cc. at Station 10245; 25 cc. at Station 10248; 75 cc. at Station 

 10250; 80 cc. at Station 10253, 35 cc. at Station 10258. Elsewhere 

 in the Gulf of Maine (Stations 10213-10215, 10246, 10247, 10249, 

 10254-10256), the volumes of the catches ranged from about 5-10 cc. 



The data for 1915 are chiefly valuable as outlining the seasonal 

 fluctuations in the two most important groups, diatoms and Cera- 

 tium. In the w^estern part of the Gulf, diatoms swarm in early spring 

 (1914b) when they fill the water almost to the exclusion of other 

 plankton, just as is the case in the Irish Sea (Herdman and Ridell, 

 1911), in the Skagerak and in the North Sea (Gran, 1915), though it 

 is not known whether the swarm then extends to the eastern shore of 

 the Gulf. In May, 1915, diatoms were still swarming over a triangu- 

 lar area in the central part of the Gulf extending from Cape Elizabeth 

 to the Grand Manan Channel, (Fig. 98), and from the coast of Maine 

 south at least as far as Cashes Ledge. But they had already been 

 replaced by Ceratiura off Massachusetts Bay, while Ceratium like- 

 wise occupied the waters over the coast bank west of Nova Scotia. 



Even the most cursory examination of the diatom swarm of May 

 shows that different genera predominated in different localities. 

 Along the shore of the Gulf (Stations 10275, 10276, 10277), the nets 

 yielded almost pure catches of Thalassiosira gravida and Th. nordcn- 

 skioUU as was the case in April 1913 (1914b, p. 405), with smaller 



