220 MEDUSA OF THE WORLD. 



Dipleurosoma is exceedingly variable in the number and arrangement of its radial-canals. 

 The Pacific species is distinguished by having marginal clubs between its tentacles, these being 

 absent ( ?) in the Atlantic Dipleurosoma typicnm. 



Dipleurosoma collapsa Mayer. 



Plate 27, figs. I to 3, and 7. 



Tftracannolatolla/>sa,MA\T.tt, 1900, Bull. Mus.Comp.Zool. at Harvard College, vol. 37, p. 46, plates 7,8, figs. 14-16; Memoirs Nat. 

 Sci. Mus. Brooklyn Inst. Arts and Sci., vol. i, No. i, p. 12, plate 4, fig. 32. MAAS, 1904, Sitzungsber. math.-phys. Klasse 

 lier kgl. Bayer. Akad. Wissenschaft., Bd. 34, p. 440. 



Adult nii-Jusa (plate 27, fig. 3). Bell J mm. in diameter and about as high as broad. 

 Tup dome-shaped, side walls vertical. 16 well-developed tentacles are carried tightly coiled 

 in close helices, and besides these there are 1 12 very small rudimentary tentacles. Dark-brown 

 entodermal pigment-spots are found within the base ot each tentacle. There are 16 radial- 

 canals, arranged in 4 groups of 4 each (plate 27, fig. 7). The gonads are found in proximal 

 parts of the 16 radial-canals very near the point where they branch off from the stomach. 

 Peduncle of manubrium wide and prominent. The mouth has 8 slightly crenated lips. 

 Entoderm of manubrium in some specimens is green, in others it is pearly-white or yellowish. 

 Entodermal pigment-spots at bases of tentacles are dark-brown. 



Stugi-s in development. The youngest medusa observed had a bell i mm. in diameter 

 (plate 27, fig. i ). It had 4 slender radial-canals and 24 tentacles, 4 well-developed and 20 

 rudimentary. Velum prominent; 4 lips, and as yet no peduncle. No trace of genital organs. 

 In the next older stage (plate 27, fig. 2), we find 4 new radial-canals beginning to develop. A 

 still older stage (plate 27, fig. 7) has 16 radial-canals and 8 lips, but as yet no peduncle and no 

 trace of gonads, nor have radial tubes grouped themselves into 4 bundles as in the adult. 



This medusa is very common at the Tortugas and Bahamas in June, and ample oppor- 

 tunity for observing its transformation was afforded. It exhibits the curious habit of collap- 

 sing into an almost shapeless mass, in which condition it may remain tor several hours and 

 then "straighten out" and swim about in excellent condition. 



Fewkes, 1883 ("On a Few Medusa? from the Bermudas," Bull. Mus. Comp. Zool., 

 vol. ii, No. 3, figs. 7, 70), has evidently figured the young of this species under the name of 

 "Larva of an unknown Tubularian." 



Dipleurosoma ochracea sp. nov. 

 Plate 29, figs. I and 2. 



Immature medusa. Bell thin-walled, somewhat flatter than a hemisphere and 8 mm. in 

 diameter. About 12 to 16 well-developed tentacles and about 35 immature or rudimentary 

 tentacle-bulbs. The well-developed tentacles are in the radii of radial-canals. They have 

 hollow, conical, basal bulbs and filiform, contractile, lash-like shafts, which are about as long 

 as the bell-radius. Each tentacle-bulb is flanked by a pair of large, sausage-shaped, marginal 

 clubs, and in addition to these there is a single sausage-shaped diverticula from the ring-canal 

 on the subumbrella side above each tentacle-bulb. There are no marginal cirri or append- 

 ages other than those described above. Velum very wide. Central stomach is flat and about 

 one-fifth as wide as bell-diameter. About 6 to q radial-canals arise in a very irregular man- 

 ner from margin of stomach; some of these give rise to side branches. Manubrium very 

 shallow, 6 or more very irregularly arranged, folded lips with plain margins. No gonads are 

 observed, though they may develop later upon the broad, expanded middle regions of the 

 radial-canals. Stomach, radial-canals, and marginal clubs of this medusa are crowded with 

 masses of yellow algae, or Philozoon, apparently similar to that which infests the medusae of 

 / elella. These plant-cells develop between the cells of the medusa and give a dense, opaque, 

 brilliant yellow coloration to the marginal clubs, and in a lesser degree to the stomach and 

 canals. All other parts are colorless. 



The medusae are remarkable for their very active, incessant pulsation. 



Large swarms of this medusa appeared at Tortugas, Florida, between July 5 and 24, 1907, 

 but no mature specimens could be found. 



