376 
BULLETIN OE THE BUREAU OF FISHERIES 
a large Bolinopsis is completely absorbed by a Beroe in four or five hours’ time 
(L. Agassiz, 1860, p. 274). Copepods, also, are often found in its digestive cavity. 
Beroe, like all the other pelagic animals that inhabit the gulf throughout the 
year and are widely distributed there vertically as well as horizontally, necessarily 
experiences nearly the whole gamut of temperatures and salinities that prevail there 
at one season or another; and although its habit of sinking in winter results (whether 
voluntarily or not) in its avoiding the very coldest water, with 2 to 3° the lower limit 
to its regular occurrence in the gulf, it has been found living actually among the ice 
in the Arctic Ocean (Mortensen, 1912), apparently thriving, to judge from the large 
size of the specimens in question. Nor does heat act as a barrier to its vertical migra- 
tions within the extremes normal to the gulf— witness how often it comes to the 
surface on calm days in summer and how abundantly it spawns at that level at the 
season when the gulf as a whole is at its warmest. Beroe is equally catholic with 
respect to salinity, except that it has not been found in the very freshest water of the 
gulf at the time of the spring freshets — that is, in salinities lower than about 31 per 
mille. 
Other ctenophores 
No other ctenophores have actually been recorded of recent years within the 
geographic confines of the Gulf of Maine as here limited. Another lobate species, 
Lesueuria Tiyboptera, was described by A. Agassiz (1865) from Massachusetts Bay, 
but has never been seen since. Mayer (1912, p. 20) has suggested that it was actually 
Bolinopsis with the oral lobes torn off and the edges healed over to produce a rounded 
contour, he having seen many in that condition in Halifax harbor after a storm. Its 
status remains problematical. 
Mnemiopsis leidyi, a southern neritic form very abundant along the coasts of the 
middle Atlantic States, is common as far north as the Woods Hole region during some 
summers, but it has never been known to round Cape Cod. 
The Venus’ girdle ( Cestum veneris ) was taken off the southeastern slope of 
Georges Bank in 1872, among an assemblage of other tropical plankton (Smith and 
Harger, 1874). 
SlPHONOPHORES 
Although the siphonophores are well represented in the warm oceanic waters 
off the continental slope abreast of the Gulf of Maine, only one member of this 
group of oceanic coelenterates — StepJianomia earn — is anything but a rare stray 
within the latter. It is probable that the low salinity of the gulf, as much as its 
comparatively low temperature, makes it inhospitable to siphonophores, for, as I 
have previously pointed out (Bigelow, 1911a, p. 381), they “are almost a negligible 
factor in the plankton in waters with a salinity less than 35 per mille” and “are 
entirely absent when the salinity is below about 30 per mille,” a generalization that 
applies as well to the North Sea region on the eastern side of the North Atlantic 
as to North American coastal waters on the western. 
