CTENOPHORES OF THE ATLANTIC COAST OF NORTH AMERICA 19 



Genus LESUEURIA Milne-Edwards, 1841. 



Lesueuria, Milne-Edwards, H., 1841, Annal. des Sci. Nat., s6r. 2, tome 66, p. 

 199. — Lesson, 1843, Hist. Zooph. Acal., p. 90.— Agassiz, L., i860, Cont. Nat. 

 Hist. U. S., vol. 3, p. 290. — Agassiz, A., 1865, North Amer. Acal., p. 23. — 

 Chun, 1880, Ctenophoren des Golfes von Neapel, pp. 290, 291. — VanhOffen, 

 1906, Nordisches Plankton, Ctenophoren, p. 4. — Moser, 1908, Abhandl. 

 Akad. Mtinchen, Suppl. Bd. r, Abhandl. 4. 



GENERIC CHARACTERS. 



Lobatae with rudimentary oral lappets and with long, ribbon-shaped 

 auricles. The peripheral gastro-vascular system is simple, without 

 complex windings. 



The type species is Lesueuria vitrea of the Mediterranean. 



The so called American species L. hyboptera is said to be more nearly 



rectangular in outline than the oval-shaped L. vitrea of Europe. In the 



American form the body is wider both above and below than it is in the 



middle, thus giving it somewhat the appearance of a laterally flattened 



hour-glass. 



Lesueuria hyboptera A. Agassiz. 



Lesueuria hyboptera, Agassiz, A., 1865, North Amer. Acalephas, p. 23, figs. 25-28. — 

 Vanhoffen, 1895, Bibliotheca Zoologica, Heft 20, Lfg. i, p. 18. 



The body of the adult animal is loo mm. long, while the broad side 

 (stomodaeal axis) is 50 mm. and the narrow side (funnel-axis) is 30 mm. 

 The lateral compression is thus almost as great as in Mertensta, but of 

 reverse character, the gastric axis of Mertensia being the narrower. 

 The body is widest at about the level of the mouth. The apical sense- 

 organ lies at the bottom of a narrow cleft about 12 mm. in depth. The 

 4 subtentacular rows of ciliated combs are each about half as long as the 

 body and terminate near the bases of the 4 auricles. These auricles are 

 very large, being almost 50 mm. in length. They are wide and ribbon- 

 shaped and their free edges are lined with a row of hair-like cilia. The 

 4 subventral rows of ciliated combs are longer than the 4 subtentacular 

 rows and extend over fully three-fourths of the length of the body. The 

 2 oral lappets are short and blunt, being not more than one-tenth as 

 long as the body of the animal. This bluntness imparts an almost rec- 

 tangular appearance to the creature when seen from the broad side. 

 The stomodaeum is long and narrow, while the funnel-tube is very short. 

 The tubes of the peripheral canal-system are extremely narrow and 

 exhibit no complex windings. The 4 subtentacular meridional vessels 

 wind somewhat as they enter the auricles, while the 4 subventral merid- 

 ional tubes are quite straight and do not wind as they extend through 

 the substance of the oral lappets. The animal is almost transparent, 

 being of a slightly milky hue. It gives rise to an intense steel-blue 

 phosphorescence when disturbed at night. 



This species must be a very rare and occasional visitor to our 

 coast. A. Agassiz found it in great numbers in Massachusetts Bay and 

 Newport Harbor about i860, but it has never been seen since that time. 

 It is interesting to notice that M'Intosh, 1888 (Ann. and Mag. Nat. Hist., 

 ser. 6, vol. 2), reports the sudden appearance of great swarms of a species 

 of Lesueuria, possibly Bolinopsis ?, off the coast of Scotland. The fore- 

 going description is derived entirely from A. Agassiz, who is the only 



