RHIZOSTOM^ — RHIZOSTOMA. 699 



having but a single filament (a terminal one) on each mouth-arm, while in Rhopilniin there 

 are, in addition to the terminal knob, many lateral appendages between the frilled mouths. 

 The varieties of Rhizostoma are known only from the Mediterranean, Red Sea, and At- 

 lantic coasts of Europe and Africa, and are closely related to R. pulmo of the Mediterranean; 

 distinguished one from another only by the relative lengths, and the various shapes of the 

 terminal clubs. 



Rhizostoma piilmo Agassiz. 

 Plate 73, fig. i. 



Polta marina, .^ldrovandi, 1642, Zoophyt. Lib., tome 4, pp. 73, 76. Also; Pulmo marinus, pp. 75, 77. 



Medusa pulmo, Macri, '1778, Atti Real. Acad. Sci. Napoli, vol. 2, p. 45, tav. i.— Linne, (Gmclin), 1788, Systema Natura, Eil. 13, 

 Pars. 6, p. 31 i^ij. 



Rhizostoma aldrovaiidi, Peron et Lesueur, 1809, Annal. du Mus. Hist. Nat. Paris, tome 14, p. 362, No. 102.— Delle Chiaje, 

 1822, Mem. .\nim. senza Vert., Regno Napoli, tav. 74, fig. 10; tav. 75, figs. l-io; Ibid., 1841, vol. 7, tav. 142, 143. 



Cefihea aldrovandi, de Lamarck, 1816, Syst. Anim. sans. Vert., tome 2, p. 517. 



Rhizostoma cuvieri, Chamisso et Evsenhardt, 1821, Nova Acta Acad. Nat. Cur., Leop. C, tome 10, p. 377, plate 34.— de 

 Blainville, 1834, Manuel dWctinologie, p. 297, planche 44, fig. i. 



Rhizostoma pulmo, Agassiz, L., 1862, Com. Nat. Hist. U. S., vol. 4, p. 150.— Claus, 1883, Untersuch iibcr Organisation und 

 Entwick. der Medusen, p. 43, taf. 12-15, fign. 86, 105 (development of tlie ephyra).— Graeffe, 1884, Arbeit. Zool. Inst. 

 Wicn, Bd. 5, p. 343 (seasonal distribution). — Vanhoffen, 1888, Bibliotheca Zoologica, Bd. I, Heft. 3, p. 31. — de Vescovi, 

 1895, Zool. Results, vol. I, p. 37.— von UexkOll, 1901, Mitth. Zool. Sta. Neapcl, Bd. 14, p. 620 (rhythmical pulsation).— 

 Bethe, 1903, Allgemeine Anat. and Physiol. Nen'ensyst., pp. 87, 90, loS, 410, 426, 432, etc., fign. 33-35, 83, 87, etc. (rhvth- 

 mical pulsation); 1908, .\rchiv fiir Ges. Physiologie, Bd. 124, p. 541; Ihld., 1909, Bd. 127, p. 219. — Hargitt, 1904, Journal 

 of Exper. Zool., Baltimore, vol. i, p. 73, figs. 1-6 (regeneration). 



Rhizostoma cuvieri, Brandt, A., 1870, Mem. Acad. Sci. St. Petersbourg, tome 16, No. 6, 29 pp., I taf. (detailed description).— 

 Claus, 1877, Denkschrift. Wien Acad., Bd. 38, p. 47, plate 10, 11; 1881, Zool. .^nzeiger, Bd. 4, p. 79 ()'°""B i^pl'y"), 

 1883, Arbeit. Zool. Inst. Wien, Bd. 5, p. 9, taf. 2, fig. 12 (young ephyra); 1884, .Arbeit. Zool. Inst. Wien, Bd. 5, p. 169; 

 taf. 2, fig. 12 (ephyra).— Blanchard, 1883, Zool. Anzeiger, Bd. 6, p. 67 (the blue coloring matter is not cyancin).— Hesse, 

 1895, Zeit. fiir wissen. Zoo]., Bd. 60, p. 411, taf. 20-22 (ner\'ous system and sense-organs). 



Pilema pulmo, Haeckel, 1880, Syst. der Medusen, p. 591 (record of literature).— Hamann, 1881, Jena. Zeit. fiir Naturwissen, 

 Bd. 15, p. 250, taf. 10, fii;. 13 (structure of mouth-arms). 



Bell pyriform, somewhat higher than a hemisphere, usually not more than 150 mm. in 

 diameter, though specimens 600 mm. wide may occasionally be found. Surface of exumbrella 

 fineh' granular, being covered with small nettling-warts. 8 marginal sense-organs, each 

 containing an orange-colored mass of concretions of entodermal origin; no ocellus, .'\bove 

 each sense-organ on the e.xumbrella side is a wide triangular pit, the bottom of which exhibits 

 diverging furrows. Each sense-organ is flanked by a pair of narrow, elongate, lanceolate, 

 sharp-pointed rhopalar lappets. 8 evenly rounded, velar lappets, all similar each to each in 

 size and shape in each octant. Thus there are in all 80 marginal lappets (16 rhopalar + 64 

 velar). 



The total length of the mouth-arms, including their terminal clubs, is about equal to the 

 bell-diameter. In its upper part the arm-disk is 4-sided and narrow, but below it widens out, 

 becomes 8 to 16-sided and gives rise to the 16 (8 pairs) short, simitar-shaped scapulets 

 having fringed mouths upon their upper, convex sides. The 8 mouth-arms are each 3-winged, 

 or Y-shaped in cross-section, two of the wings being directed outward, one being centripetal. 

 These wing-like expansions bear numerous mouths, the lips of which are fringed by a row of 

 short, flexible, knobbed tentacles. 



The terminal knobs are triangular in cross-section, somewhat contracted in the middle 

 of their lengths and with a simple, central canal. They are usually a little shorter than the 

 upper arms, but may equal or slightly exceed them in length. The mouth-bearing, lower 

 arms are somewhat shorter than the free upper arms between the zone of the 16 scapulets 

 and the winged portion of the arms. Ordinarily the scapulets are hidden away under the con- 

 cavity ot the subumbrella. The 4 subgenital pits are narrow, slit-like and with their open- 

 ings constricted in the middle by a knob-shaped protuberance upon the floor of the subum- 

 brella. The 4 invaginated, genital sacs are small and separated completely one from another. 



The cruciform central stomach gives rise to 16 radiating canals, 8 of which extend to the 

 sense-organs and 8 are intermediate in position; all reach the bell-margin. A network of 

 anastomosing vessels places the outer halves of the radial-canals in connection one with 

 another, and e.xtending inward between the 16 radial-canals are 16 blindly ending areas 

 composed of a network of vessels. There is no distinct ring-canal at the bell-margin, but 

 the connections between the radial-canals are wider along the inner edge of the zone of anas- 

 tomosing vessels than elsewhere. 16 deltoid areas of circular muscles alternate with the 

 radial-canals and are more or less completely separated in the radii of the canals themselves. 



