PLANKTON 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 
Fig. 43. — Occurrence of the pteropod Limacina retroversa from July to September, 1912 to 1922. a , occurred; ©, swarmed; 
O, not taken 
our records are most extensive) it has appeared at rather more than half of all the 
stations, hut 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, 
