PLANKTON OF THE GULF OF MAINE 57 



numbers of large Salpse (probably S. tilesii) in Massachusetts Bay in November 

 and December, 1913, which, so far as I can learn, are the only occasions when 

 Salpsa have been found in such numbers within the gulf, though they are often reported 

 in abundance south and west of Cape Cod. Local swarms, such as this, probably 

 result from their very rapid asexual multiplication (there is no evidence that they 

 can reproduce sexually in cool waters) in summer and early autumn (A. Agassiz, 

 1866). 



The Portuguese man-of-war (Physalia) , with its translucent float, is even more 

 apt to attract attention than Salpa, as it drifts on the surface, and it is equally a 

 tropical visitor, though at the mercy of wind as much as of current. We have only 

 one record of Physalia within the gulf, viz, in the eastern basin, June 19, 1915 

 (Bigelow, 1917, p. 246; a single specimen seen but not captured). In the summer of 

 18S9, however, a year when Physalia was unusually plentiful off the coast of southern 

 New England, many were seen in the Bay of Fundy and several were taken near 

 Grand Manan and submitted to Doctor Fewkes for identification (Fewkes, 1889 

 and 1890). The only other tropical coelenterates so far recorded within the gulf 

 are two examples of the siphonophore Physophora hydrostatica on German Bank 

 (station 10030) in August, 1912 (Bigelow, 1914, p. 103), 28 while the "Venus girdle" 

 (Cestum), a warm-water ctenophore, is known from off the southeast slope of Georges 

 Bank (Smith and Harger, 1874; Bigelow, 1914b, p. 31). 



We have one record for a tropical pteropod (Limacina inflata) off Cape Cod on 

 July 19, 1914 (station 10213), while two living specimens of the pteropods Diacria 

 trispinosa and Atlanta, genera that are of warm Atlantic if not strictly tropical 

 origin (Meisenheimer, 1905), were taken in a haul near Gloucester on July 8, 1913. 

 The warm-water hyperiid amphipod Phronima sedentaria was taken on Browns 

 Bank on June 24, 1915 (station 10296), which, with a fragment of gulfweed near 

 German Bank (September 2 of that year), completes the list. 



The geographical locations of these records, the most characteristic of which are 

 shown on the accompanying chart (fig. 31), and their dates prove that occasional 

 planktonic immigrants from the inner edge of the Gulf Stream may be expected 

 anywhere in the Gulf of Maine at any season. Aside from Thysanoessa gregaria, 

 however, which may, perhaps, be endemic in small numbers in our waters, or which 

 at least is able to survive there for a long time if it does not reproduce (p. 143), and 

 omitting Sagitta seiratodentata, which falls in a different category (p. 58), there is a 

 decided preponderance of tropical records in the eastern part of the gulf, though 

 fewer hauls have been made there than in the western, a concentration, that is to 

 say, where the salinity curves locate the chief influx of offshore water. The great 

 majority of the records lie in the peripheral zone corresponding to the anticlockwise 

 oceanic eddy that dominates the circulation of the gulf. 



In spite of the considerable tropical list, we have never made anything that could 

 be called a tropical haul in the gulf or encountered a community of animals of warm- 

 water origin there. In fact, most of the records are for single specimens; seldom has 

 the tow net yielded as many as half a dozen at any one station, and, except for certain 



» Also taken off the southern face of Georges Bank on July 24, 1916, station 10352. 



