plankton of the gulf of maine 129 



Other pelagic mollusks 



Apart from the cephalopoda and the three pteropods (Limacina retroversa, L. 

 Jtelicina, and Clione limacina) just discussed, very few adult pelagic Mollusca have 

 ever been found within the southern rim of the Gulf of Maine. 08 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 

 injiata 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 particidar 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 Ptero trachea 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 were 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. 



88 Leaving out of account the various pelagic bivalve and gastropod larvae. 



