MEDUSAE OF THE WORLD. 



caulus. The hydrocaulus is corrugated and opaque in color throughout its length, and in 

 this respect differs from the European G. nnplcxa Allman, 1871. The fully developed 

 hydranths are only 1.5 mm. in height. They are elongate, spindle-shaped, and taper gradually 

 from near the base to the summit, so that the diameter near the mouth is less than that near 

 the base. The tentacles arise in 5 to 8 well-defined whorls from sides of hydranth, each whorl 

 consisting of 4 to 6 tentacles. These tentacles are short and taper from base to end, termi- 

 nating in a large knob containing nematocysts. The entodermal cores of the tentacles are 

 composed of vacuolated cells. The tentacles are stiff and project rigidly outward from the 

 sides of the hydranth. 4 to 8 medusa-buds in various stages of development arise from the 

 sides of the hydranth near the base immediately below the lowest whorl of tentacles. 



When set free the young medusa (plate 8, fig. 3) has 2 well-developed, radially situated, 

 diametrically opposed tentacles, and 2 rudimentary tentacle-bulbs. There are 4 radially 

 situated, nematocyst-bearing ridges upon the exumbrella, and these extend about half-way 

 up the sides of the bell. The bell-walls are very thin and flexible. There are 4 straight, 

 narrow radial-canals, and the manubrium is a short, simple tube with no trace of the gonad. 

 The mouth is a simple, round opening. Before being set free the tentacles are coiled inward 

 so as to lie within the bell-cavity. Soon after the medusa has become liberated, however, 

 the tentacles uncoil and project outward. The deep-lying entoderm of the hydranths is a 

 delicate creamy-pink, while the more superficial entoderm is translucent and milky in color. 

 The cells of the superficial entoderm are large and vacuolated. The hydrorhiza and hydro- 

 caulus is protected by a horny, yellow, amber-colored, chitinous sheath, but this does not 

 extend over the hydranths. The hydroid was found at Tortugas, Florida, in June, 1899, 

 growing upon a piece of floating gulfweed (Sargassum). 



Zanclea gemmosa McCrady. 



Plate 6, fig. 7; plate 7, fig. 5; plate 8, figs. 4 and 5. 



Gemmaria gemmosa, McCRADV, 1857, Gymn. Charleston Harbor, p. 49. 



Zanclea gemmosa, McCRADV, 1857, Gymn. Charleston Harbor, p. 49, plate 8, figs. 4, 5. AGASSIZ, L., 1862, Cont. Nat. Hist. 



U. S., vol. 4, p. 344. HARTLAUB, 1907, Nordisches Plankton, Nr. 12, p. 121, fign. 116, 117. 

 Gemmaria gemmosa, AGASSIZ, A., 1865, North Amer. Acal., p. 184, fig. 306. HAECKEL, 1879, Syst. dcr Medusen, p. 104. 



FEWKES, 1881, Bull. Mus. Comp. Zool. at Harvard College, vol. 8, No. 8, p. 150, plate i, figs. 8-12. FEWKES, 1884, 



American Naturalist, vol. 18, p. 196, fig. 2. 

 Corynitis agassizii (hydroid), MURBACH, 1899, Quart. Journ. Micr. Sci., vol. 42, p. 354, plate 34, fig. 12 (medusa, figs, n, 



I3 H-) 



Gemmaria sagiltaria, HAECKEL, 1879, Syst. der Medusen, p. 103, taf. 7, figs. 3, 4 (young medusa). 

 Zanclea gemmosa (hydroid), WALLACE, 1908, Carnegie Institution Year Book, No. 7. 



Adult medusa. Bell 6 mm. in height, and pynform. There is a well-developed, solid, 

 apical projection. Side walls quite thin. There are 4 long, radially situated tentacles with 

 large, hollow basal bulbs, which lack ocelli. The shafts of the tentacles are crowded with 

 large numbers of short filiform branches, which arise only from the dorsal (exumbrella) 

 side of the tentacles, although the twisting of the tentacle may cause them to appear to arise 

 from all sides. Each of these filiform branches terminates in a large spear-head-shaped 

 body which bears a number ot long, delicate, sharp-pointed bristles, and which contains 

 3 to 9 egg-shaped nematocyst-cells. A club-shaped swelling extends longitudinally from 

 the base of each tentacle a short distance up the side of the exumbrella. These swellings are 

 thickly covered with nematocysts. There are 4 straight, slender radial-canals, and a narrow 

 circular vessel. The velum is wide and delicate. The manubrium is flask-shaped, and cruci- 

 form in cross-section and extends to the level of the velar-opening. The mouth is a simple, 

 cruciform opening without prominent lips. The gonad is upon the sides of the stomach. 

 These sides are greatly swollen and give to the manubrium its flask-shaped appearance. 

 The entoderm of the manubrium and tentacles is of a delicate creamy-pink and the ectoderm 

 of the manubrium is of a delicate shade of green. 



Young medusa (plate 7, fig. 5; plate 8, figs. 4, 5). In the medusa, I mm. in height, 

 there are but 2 marginal tentacles. The bell-walls are very thin and the manubrium is a 

 simple fusiform tube. There is no apical projection to the bell, and no trace of gonads upon 

 the manubrium, and the mouth is a simple, round opening without cruciform lips. 



This species extends from the West Indies to the southern coast of New England. It is 

 quite common in Newport Harbor late in the summer. 



