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 !1915 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 10489, 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 typically 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 
