10 CTENOPHORES OF THE ATLANTIC COAST OF NORTH AMERICA 



Pleurobrachia pileus Vanhoffen. 



Beroe pileus, Fabricius, 1780, Fauna Gronlandica, p. 361, Nr. 354. 



Beroe globigereux, Cuvier, 1817, Regne Animal, tome 4, p. 59. 



Cydippe pileus, Gould, 1841, Report Invert. Mass., p. 349. — MOrch, O., 1857, 

 Beskriv. a£ Gronland, p. 97. 



Pleurobrachia rhododactyla, Agassiz, L., 1849, Mem. American Acad., vol. 4, part 

 10, p. 314, plates I to 5; ibid., i860, Cont. Nat. Hist. U. S., vol. 3, pp. 203, 

 294; plate 20. — Stimpson, W., 1853, Marine Invert. Grand Manan, p. 11. — 



y^ Agassiz, A., 1865, North Amer. Acal., p. 30, figs. 38 to 51; Ibid., 1874, Mem. 

 / American Acad., vol. 10, No. 3, pp. 372 to 374, plate 3, figs. 25, 25'; plate 4,. 

 figs. I to 45; plate 5, figs. I to 32. — Fewkes, 1884, Mem. Museum Comp. 

 Zool. at Harvard College, vol. 9, No. 3, plate 9, figs. 8 to 9, 14 to 37. 



Pleurobrachia rhododactyla and P. pileus, VanhOffen, E., 1895, Bibliotheca Zoo- 

 logica. Heft 20, Lfg. i, pp. 15, 17, 21. — Curreri, 1900, Boll. Soc. Ital. Zool.^ 

 Roma, Anno 9, p. 192. 



Pleurobrachia pileus, Chun, C, 1898, Ergeb. der Plankton-Expedition, Ctenophoren, 

 p. 15. — Grabe, 1901, Zeit. fiir wissen. Zool., Bd. 69, p. 486, Taf. 36, 37 (develop- 

 ment of sexual organs). — ROmer, 1903, Fauna Arctica, Ctenophoren, Bd. 3, 

 p. 75 (full list of literature). — Moser, 1903, Ctenophoren der 5i6ofa-Expedi- 

 tion, p. 5 (list of literature); also, 1908, Zool. Anzeiger, Bd. 33, p. 756. — 

 Parker, 1905, Journal Experimental Zool., vol. 2, p. 409 (movements of 

 swimming plates, see Mnemiopsis). — Browne, 1905, Proc. Royal Soc. Edin- 

 burgh, vol. 25, p. 784. — Moser, 1909, Ctenojjhoren der deutsche Sudpolar- 

 Exped., Bd. 11, p. 141. — Ghigi, 1909, Ctenofori, Roy. Instituto Studi Supe- 

 riori, Firenze, vol. 2, fasc i, p. 9. — Evans and Ashworth, 1909, Proc. Roy. 

 Physical Soc, Edinburgh, vol. i7,»p. 308. 



Pleurobrachia bachei, Agassiz, L., i860, Cont. Nat. Hist. U. S., vol. 3. p. 294. — 

 Agassiz, A., 1865, North American Acal., p. 34. — ^Torrey, 1904, Univ. 

 California Publications, Zool., vol. 2, p. 46, plate i, fig. 3. 



The body is egg-shaped, or almost spherical, and about 17 to 20 

 mm. in length and 14 to 18 mm. wide in the tentacular axis. Evans and 

 Ashworth, 1909, record a specimen 30 mm. in length from Burntisland 

 Harbor, Scotland, in December. It is only slightly compressed later- 

 ally in the plane transverse to the tentacular diameter, so that the 

 lateral diameters are to each other as about 10 to 12.5, the tentacular 

 axis being the wider. The apical sense-capsule is situated upon the 

 surface and is not sunken within a niche. It incloses a small, spherical 

 mass of concretions and is not surrounded by protuberances, the 

 outer surface of the apical pole-plate being smooth. The eight rows 

 of ciliated plates are about equal in length each to each and extend 

 from points quite near the apical sense-organ, about three-quarters the 

 distance down the sides of the body. Each subtentacular row contains 

 about 38 combs of cilia, and each sub ventral row 35. The 2 tentacles 

 arise from 2 deep clefts in the sides of the body which serve as sheaths 

 into which the entire contractile portion of the tentacles may be with- 

 drawn. The tentacle-bulbs are widely separated from the sides of the 

 paragastric canals. When they are fully expanded the tentacles may be 

 15 to 20 times as long as the body and have a linear row of numerous sim- 

 ple, lateral filaments which give them a delicate, feathery appearence. 

 They are highly contractile and extremely sensitive and are constantly 

 changing their appearance as the animal moves through the water, at 

 times being drawn up into knotted, string-like masses, and at other 

 times being stretched far out in graceful, sweeping curves with their 

 lateral filaments giving them the appearance of the most exquisite one- 

 sided feathers. The mouth is a long, narrow slit, its wide axis being 

 perpendicular to the plane passing through the tentacles. The stomo- 



