444 BULLETIN OF THE BUREAU OF FISHERIES 



Rh. semispina certainly is no more neritic in the Gulf of Maine than it is off 

 north European coasts, where it is commonly regarded as oceanic, and I may hazard 

 the guess that its occasional abundance in waters as shoal as those of German and 

 Georges Banks and off Marthas Vineyard reflects local hydrographic conditions 

 exceptionally favorable for its growth and reproduction, not any dependence on its 

 part on the bottom below or on the neighboring coast line. Nevertheless, the 

 presence of Rh. semispina is not a reliable index to offshore water, because it may be 

 able to thrive in coastwise regions "several years after the inflow of oceanic water has 

 taken place," as Ostenfeld (1913, p. 443) has remarked. In short, from the distribu- 

 tional standpoint Rh. semispina is intermediate between the typically oceanic Rh. 

 styliformis and the strictly neritic Rh. setigera (p. 446), these three species bearing 

 the same relationship to one another in the Gulf of Maine as on the other side of 

 the North Atlantic. A fuller knowledge of the degree to which Rh. semispina is 

 endemic within the limits of the gulf, or is immigrant thither from elsewhere, is much 

 to be desired. 



Only two other species of Rhizosolenia have so far been detected with any 

 regularity in the collections from the open Gulf of Maine — Rh. styliformis and Rh. 

 setigera (fig. 128). Rh. styliformis has been but sparsely represented in the tow 

 nettings north of Georges Bank. In March, 1920, it was not found there at all; in 

 April of that year it was noted (occasional specimens) off Cape Cod (station 20088). 

 at the mouth of Massachusetts Bay (station 20090), and in the Northern Channel 

 (station 20105). We did not detect it at all in the gulf north of the banks in May 

 either in ;19 15 or in 1920, and only once in June, 1915 (station 10290), and have 

 only one summer record of it in the inner parts of the gulf — viz, off Lurcher Shoal 

 on August 12, 1914 (station 10245). It appeared in small numbers at three out of 

 five stations near Massachusetts Bay from November 1 to 8 in 1916 (station 10400 

 north of Cape Ann and stations 10401 and 10403 off Massachusetts Bay), likewise 

 off Cape Ann, off Cape Cod, and in the Western Basin on December 29 and 30, 1921 

 (stations 104S9, 10490, and 10491), suggesting a period of augmentation in autumn 

 and early winter either by propagation within the gulf or, as is more likely, by immi- 

 gration from offshore. Similarly, Fish (1925) found it only in winter at Woods Hole, 

 and very scarce even then. Evidently it is rare in the Bay of Fundy, for while Bailey 

 (1915) notes it for St. Andrews, McMurrich found it on one occasion only, and Fritz 

 (1921) does not list it there at all. 



Rh. styliformis is far more important in the plankton over the offshore banks 

 than it is in the inner parts of the gulf, as might be expected from its typicalry oceanic 

 nature. For example, the Grampus found it in abundance on the western part of 

 Georges Bank in July, 1913 (station 10059), and again in July, 1916 (stations 10347 

 and 10348), and likewise over the northeast part of the bank in that same month in 

 1914 (station 20223). It also occurred generally from off Nantucket out to the con- 

 tinental slope of Georges Bank in July, 1916 (stations 10349, 10351, and 10354 

 to 10356). Although we did not detect Rh. styliformis anywhere on the bank (or 

 on Browns Bank either, for that matter) in March, April, or May of 1920, it domi- 

 nated the pelagic flora over the northern part of Georges Bank on the 27th of April 

 in 1913, when "many of the specimens were so large (1.1 millimeters) as to be easily 



