PLANKTON OF THE GULF OF MAINE 
125 
Limacina helicina Phipps 
The Arctic pteropod L. helicina, a close relative of the boreal L. retroversa, 
though characteristic of a different zoogeographic province, appears but rarely in the 
gulf, and then only as an immigrant from the colder waters to the east and north. 
Its status as such and its importance as an indicator of cold currents being discussed 
elsewhere (p. 59), this mention may be confined to a list of its recorded occurrence in 
the Gulf of Maine. 68 
May 6, 1915 — off Cape Sable, station 10270, 150-0 meters and 50 meters. 
May 10, 1915 — near Lurcher Shoal, station 10272, 60-0 meters, occasional specimens 
on each occasion. 
Clione limacina (Phipps) 
The large shell-less pteropod Clione, beautiful in the water and easily recog- 
nized, may be expected anywhere in the northern half of the Gulf of Maine in winter, 
spring, or summer (fig. 45). During the cold half of the year — December to May — 
it has appeared at nearly 50 per cent of our stations, both over the gulf as a whole 
and on the individual cruises. Not only are the records for these months very 
generally distributed over the deeper basins and along the coastal belt, but Clione 
may be more universal than the actual records suggest, for we have usually taken it in 
numbers so small that its failure to appear in the tow nettings at other stations may 
have been purely accidental. 
In summer, too, we have found Clione repeatedly in the northern parts of the 
gulf, but during the period from June to August it has appeared at only about 20 
per cent of our stations — that is, distinctly less regularly than in winter or spring. 
We have not found it at all in September, October, or November, though the few 
stations for those months have been occupied at localities where it has been taken at 
other times of year. From this it appears that Clione is distinctly seasonal in its 
occurrence in the gulf, reaching its maximum from February until May and its 
minimum in autumn. 
Although Clione is oceanic in its general biologic status as opposed to neritic or 
coastwise, it shows no apparent predilection for the deeper rather than the shoaler 
parts of the Gulf of Maine; and while we have not found it in inclosed waters, and 
Doctor McMurrich detected it only once at St. Andrews (on February 16, 1916), 
it has been known to appear in swarms in Portland Harbor, an event referred to below 
(p. 127). Neither do our records suggest any seasonal onshore or offshore migrations 
on its part, such as appear to be executed by its relative, Limacina retroversa. 
I should point out that Clione is no more regular in its occurrence and shows 
no more concentration in the eastern than in the western side of the gulf, such as 
might be expected of an organism the maintenance of whose numbers within our 
limits depends partly on immigrations around Cape Sable, and such as actually ob- 
tains for various Arctic animals (p. 59). On the contrary, no general portion of the 
open gulf north of a line from Cape Cod to Cape Sable appears more favored by it 
than another at its season of maximum abundance, but our few traverses of Georges 
8E Also oil Halifax, Aug. 2, 1914; near Shelburne, Nova Scotia, and over the continental slope off that port, June 23 and 24, 1915 
(Bigelow, 1917, p. 300). 
8951—28 9 
