CTENOPHORES OF THE ATLANTIC COAST OF NORTH AMERICA 9 



smooth-edged polar plate, there being no wing-like protuberances, such 

 as are seen in Beroe. 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 simimer 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 Beroe octopiera described by Mertens, 1833 (Mem. Acad. 

 Nat. Sci. St. P^tersbourg, s^r. 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, p. 612; also, Hist. British 

 Animals, 1828, p. 504. — Agassiz, L., 1849, Mem. American Acad., vol. 4, p. 

 314; also i860, Cont. Nat. Hist. U. S., vol. 3, p. 203. — Agassiz, A., 1865, North 

 Amer. Acalephae, p. 29. — Chun, 1880, Ctenophoren des Golfes von Neapel, 

 p. 281. — Chun, 1898, Ctenophoren der Plankton-Expedition, p. 15. — ^Van- 

 hOffen, 1906. Nordisches Plankton, Ctenophoren, p. 3. — Moser, 1903, 

 Ctenophoren der 5i6oga-Expedition, pp. 5, 30; 1909, Ctenophoren der deutsche 

 Siidpolar-Exped., Bd. 11, Zool. 3, p. 141. 



Cydippe, Eschscholtz, 1829, Syst. der Acal., p. 29. — Lesson, 1843, Hist. Zooph. 

 Acal., p. 104. 



GENERIC CHARACTERS. 



Cydippidae 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. 



