PLAKKTON OF THE GULF OF MAINE 



117 



As appears from the accompanying charts (figs. 43 and 44), this pteropod has 

 been taken over all the offshore waters of the gulf, on Georges Bank, and over the 

 continental shelf off Nantucket. During our summer cruises (the season for which 



Fio. 43.— Occurrence of the pteropod Limadna retroversa from July to September, 1912 to 1922. • , occurred; 0, swarmed; 



Oi not taken 



our records are most extensive) it has appeared at rather more than half of all the 

 stations, but the regularity of its distribution differs from summer to summer. 

 For example, it was practically universal over the deeper parts of the gulf in August, 



