LEPTOMEDUS.E — .EQUOREA, ZYGODACTYLA. 



335 



flat and about one-half as wide as the bell-diameter. Its margin is circular and there are about 

 1 6 long, slender lips. Gonads are on the proximal halves of the radial-canals, developed on 

 the sides of the canals and laterally compressed. Found over the Pearl Banks, Gulf of Manaar, 

 between Ceylon and India. 



Genus ZYGODACTYLA Brandt, 1835, sensu Agassiz. 



Zygodactyla, Brandt, 1835, Mem. Acad. Imperiale des Sci. St. Petersbourg, Sci. Nat., ser. 6, tome 2, p. 221. — Agassiz, L., 

 1862, Cont. Nat. Hist. U. S., vol. 4, p. 360.— Agassiz, A., 1865, North Amer. Acal., p. 103. — Fewkes, 1889, Report 

 Commiss. Fish and Fisheries for 1886, p. 522. 



Rhacosioma, Agassiz, L., 1850, Proc. Boston Soc. Nat. Hist., vol. 3, p. 342. 



Pohcanna, subgenus Zygodactyla, Haeckel, 1879, Syst. der Medusen, p. 231. 



Brandt, 1835, established the genus Zygodactyla for a medusa found offthe coast of Japan, 

 called Mesonema {Zygodactyla) coerulescens. Zygodactyla graenlandica L. Agassiz, will serve 

 as the type of genus for Brandt's medusa proves to be an Mquorea. 



GENERIC CHARACTERS. 



Similar to Mquorea, but the subumbrella gives rise to rows of gelatinous, wart-like pro- 

 tuberances between the radial-canals. In Mquorea, on the other hand, the subumbrella is 

 smooth. 



In common with Mquorea, medusae of Zygodactyla appear to be highly variable, both in 

 color and in the relative number of the radial-canals, tentacles, lips, and lithocysts. The shape 

 and size of the stomach change with age and with different states of contraction. 



Were it not for the fact that the genus Zygodactyla is one of the old-established genera, 

 I would prefer to consider it merely as a subgenus of Mquorea. 



Zygodactyla groenlandica L. Agassiz. 



Plate 44, figs. I to 4. 



Medusa cequorea, Fabricius, 1780, Fauna Groenlandica, No. 357. 



Medina globular is, Modeer, 1791, Nova Acta Phys. Med., Bd. 8, p. 33. 



M-juarea gritnlandica, Peron et Lesueur, 1809, Ann. du Mus. Hist. Nat. Paris, tome 14, p. 339.— Lesson, i843,Zooph. Acal., 

 p. 313. 



Mquorea globularis, Morch, 1857, Beskriv af Greenland, p. 96. 



Rhacosioma allanthum, Agassiz, L., 1850, Proc. Boston Soc. Nat. Hist., vol. 3, p. 342. 



Zvgodactyla groenlandica, Agassiz, L., 1862, Cont. Nat. Hist. U. S., vol. 4, p. 360.— Agassiz, A., 1865, North American Acaleph:r, 

 p. 103, figs. 153-155, non fig. 156.— Verrii.l, 1873, Report Com. Fish and Fisheries, 1871-72, p. 729, plate 37, fig. 275. — 

 Fewkes, 1881, Bull. Mus. Comp. Zool. at Harvard College, vol. 8, No. 8, p. 156, plate 5, figs. 5, 6, 11, 12; 1884, Mem. 

 Mus. Comp. Zool. at Harvard College, vol. 9, No. 3, plate 5, figs. 17, 19.— Hargitt, 1904, Bull. U. S. Bureau of Fish- 

 eries, vol. 24, p. 25. 



Polycanna granlandica, Haeckel, 1879, Syst. der Medusen, p. 232. 



Southern variety (plate 44, figs. I to 4). The disk is about 115 mm. or more in diameter. 



The gelatinous substance is hyaline and rigid, being about 20 mm. thick in center and thin- 

 ning quite abruptly to the edge. Aboral surface ot disk flat or 

 slightly concave in center. 84 to 97 straight, narrow radial-canals, 

 the central portions of which contain the gonads. Velum rudimen- 

 tary. Tentacles only slightly more numerous than radial-canals, 

 long, with hollow tapering bulbs. The shafts of the tentacles are 

 flattened radially and are very flexible. The excretion papillae are 

 situated near the bases of the tentacles and at intervals between 

 them. 8 to 12 very minute lithocysts between each successive pair 

 of tentacles; each lithocyst contains 2 spherical concretions. There 

 is a single row of blunt, gelatinous, solid, rounded papillae upon the 

 subumbrella, between each successive pair of radial-canals (plate 

 44, fig. 2, />)■ Each row contains 6 to 13 papillae. Stomach broad, 

 flat, and sac-like, and terminates below in a long cylindrical 

 throat-tube. The mouth is surrounded by long, tapering oral 

 tentacles, which are equal in number to the radial-canals. 



Fig. 192— Young medusa of Z. The entoderm of the radial-canals, circular canal, gonads, 



.^"lantica after Fewkes, in and tentacles is f Qe licate madder-pink to milky-white, the 



Bull. M. C. Z. at Harvard f J 



College. stomach and mouth parts being ot a tainter hue 01 pink. 



