PLANKTON OP THE GULF OF MAINE 
129 
Other pelagic mollusks 
Apart from the cephalopods and the three pteropods ( Limacina retroversa, L. 
lidicina, and Clione limacina ) just discussed, very few adult pelagic Mollusca have 
ever been found within the southern rim of the Gulf of Maine. 68 The Grampus 
cruises have yielded an Atlanta and two specimens of the pteropod Diacria trispinosa 
from 10 miles north-northwest of Gloucester on July 8, 1913, and two of Limacina 
injlata taken off Cape Cod July 19, 1914 (station 10213). All these species are char- 
acteristic of the warmer parts of the North Atlantic, not of boreal waters, and hence 
reached the gulf as stragglers from the warm waters of the Atlantic to the south; 
but it is hard to account for their presence at the particular times and places of cap- 
ture, because “they were taken with an otherwise typical boreal assemblage of 
plankton organisms” (Bigelow, 1915, p. 306). 
A Pneumoderma, or some closely allied pteropod too young for identification, 
was taken near Lurcher Shoal on August 12, 1914 (station 10245); and, under the 
name Pseudoclione, Danforth (1907) has described a pteropod of doubtful relationship 
from Casco Bay, which showed sexual maturity combined with various larval charac- 
ters (taken August 29 and again September 5 to 8, 1902). A Cavolina tridentata and 
two Pterotrachea from the southern edge of Georges Bank, respectively on July 21 
(station 10219) and July 20 (station 10216) in 1914, complete the brief list. 
In contrast to the Gulf of Maine, the waters along the continental slope from 
the longitude of New York eastward have proved extremely rich in warm-water 
pteropods and heteropods carried thither in the sweep of the Gulf Stream, whence 
considerable lists of them W'ere obtained by the early expeditions of the Bureau of 
Fisheries (Smith and Hargar, 1874; Verrill, 1885; Johnson, 1915), as well as on our 
more recent Grampus cruises (Bigelow, 1917, p. 302). However, since it is only 
in the rarest instances that any of these find their way into the inner parts of the Gulf 
of Maine, little space need be devoted to them here. 
The captures of this category made by the Grampus in July, 1913, and July, 
1914, are noted elsewhere (p. 54; Bigelow, 1915, p. 301; Bigelow, 1917, p. 302). 
These two lists together comprise some 14 species, while Johnson (1915), in his more 
complete summary of previous records, mentions 25, representing the genera Firoloida, 
Carinaria, Atlanta, Clio, Cuvierina, Peracle, Corolla, and Glaucus. Others (e. g., 
Janthina) have also been recorded, but only from examples washed up on the beaches 
of southern New England or the outlying islands. To illustrate how seldom any 
of these oceanic Mollusca stray within the 500-meter contour and how sharply their 
range contrasts with that of their boreal relative L. retroversa , the accompanying 
chart (fig. 46), showing all records listed by Johnson (1915), is offered. All these 
are from summer and autumn. In winter and spring warm water, with its character- 
istic tropical-oceanic inhabitants, lies farther out from the continental edge. 
58 Leaving out of account the various pelagic bivalve and gastropod larvae. 
