CTENOPHORES OF THE ATLANTIC COAST OF NORTH AMERICA 9 
smooth-edged polar plate, there being no wing-like protuberances, such 
as are seen in Beroé. The 4 subtentacular rows of cilia are longer than 
the 4 subventral rows and extend fully four-fifths the distance from the 
apical plate to the oral end of the animal. The tentacles are long and 
contractile and give rise to numerous short, simple, lateral branches. 
The tentacles, rows of cilia, and pole-plate are light pink in color, while 
the genital products are of a decided shade of the same color; the male 
products being more brilliant than the female. 
When very young the body is almost spherical, the oral end, how- 
ever, being bluntly pointed. The rows of cilia are more fully developed 
than in the young Pleurobrachia of the same age, while the tentacles 
are relatively smaller and less developed and acquire their lateral branches 
later. In the young Mertensia, also, there are prominent orange pigment 
cells along the rows of cilia, and these are not found in Pleurobrachia. 
This species is found in the Arctic Ocean. It extends southward in 
winter to the New Jersey coast, becoming rarer towards the south. Young 
individuals are occasionally found during the summer months in Newport 
Harbor, Rhode Island, but the adults have never been taken south of Mas- 
sachusetts Bay. It is sometimes seen in great numbers in the harbor of 
Eastport, Maine,in September, but its true home is off the Labrador coast. 
Chun, 1898, reports that large numbers of this ctenophore were observed 
by the Plankton Expedition in the Labrador stream, and says that it is 
identical with the Beroé octoptera described by Mertens, 1833 (Mém. Acad. 
Nat. Sci. St. Pétersbourg, sér. 6, tome 2, p. 528), from Behring Sea. 
Bigelow finds that Mertensia ovum from the coast of Labrador feeds 
upon the sculpin. 
Genus PLEUROBRACHIA Fleming, 1822. 
Pleurobrachia, FLEMING, 1822, Philos. of Zool., vol. 2, Pee also, Hist. British 
Animals, 1828, p. 504.—Acassiz, L., 1849, Mem. erican Acad., vol. 4, p. 
314; also 1860, Cont. Nat. Hist. U.S., vol. 3, p. 203.—Acassiz, A., 1865, North 
Amer. Acalephe, p. 29.—CHUN, 1880, Cucoprerd des Golfes von Neapel, 
p. 281.—CHUN, 18098, pena Sea der Plankton-Expedition, p. 15.—VAN- 
HOFFEN, 1906, Nordisches Plankton, Ctenophoren, p. 3.—MosER, 1903, 
Ctenophoren der Siboga-Expedition, pp. 5, 30; 1909, Ctenophoren der deutsche 
Stidpolar-Exped., Bd. 11, Zool. 3, ee Iq. 
Cydippe, EscuscHoTz, 1829, Syst. der Acal., p. 29.—Lsson, 1843, Hist. Zooph. 
Acal., p. 104. 
GENERIC CHARACTERS. 
Cydippide with an egg-shaped body with but little lateral compres- 
sion, the tentacular diameter being only slightly wider than the sagittal. 
In this respect Pleurobrachia differs markedly from Mertensia, wherein 
the sagittal diameter is much narrower than the tentacular. The ten- 
tacle bulbs are placed within deep clefts, midway between the sides of 
the stomach and the general surface of the body. The 2 long, lateral 
tentacles give rise to numerous, simple, filamentous side branches. The 
8 meridional canals extend under and along the 8 rows of cilia and end 
blindly, not forming a closed system of tubes. 
The type species is Pleurobrachia pileus of the colder waters of the 
Atlantic, being abundant off the northern coast of Europe and America. 
Moser, 1903, gives a description of all of the so-called species, 
and in 1909 she presents a very complete list of references to literature 
and an account of the geographical range of all species. 
