292 



MEDUSjE of thk world. 



Staurophora arctica, Levinsen, 1893, Vid. Meddcl. Nat. For. Kjobenhavn, Ser. 5, Bd. 4, p. 145. — Hartlaub, 1897, Mceresunter- 



such. Helgoland, Neue Folge, Bd. 2, Heft I, Abt. 2, p. 486. 

 Staurostoma arctica, Linko, 1900, Mem. Acad. Imp. Sci. St. Petersbourg, ser. 8, tome 10, No. 3, p. 4, taf. 2, fign. 22-25 ( 0Ce H> 



and otocvsts); 1904, Zool. Anzeiger, Jahrg. 28, p. 218. 

 Staurostoma arctica, Haeckel= Staurophora laciniata, L. Agassiz, Birula, 1896, Annuaire Musee Zool. Acad. Imp. Sci. St. 



Petersbourg, tome 1, p. 342. 

 Staurophora laciniata, etc., Browne, 1907, Annals and Mag. Nat. Hist., ser. 7, vol. 20, pp. 470-472. 



Mature medusa (plate 26, fig. 6). — Bell 100 to 200 mm. wide, and 30 to 50 mm. high; with 

 thick gelatinous substance. Ahoral side smoothly rounded. 200 to 300 very short marginal 

 tentacles and a variable number of elongate, club-like, marginal appendages, probably all of 

 which are merely developing tentacles. Tentacle-bulbs hollow and conical, the free ends of 

 tentacles usually coiled in close helices. There is a single, small, dark-brown ocellus in the 

 ectoderm of each tentacle-bulb. These ocelli lie on the inner sides of the tentacle-bulbs, close 

 to the insertion of the velum. The ocelli are innervated by the subumbrella nerve-ring. The 

 marginal clubs are hollow and their lumen is continuous with the entoderm ot the circular 

 vessel. These marginal clubs are of various lengths (plate 26, fig. 5), and may usually be 

 seen in various stages of development into tentacles. 



Above the base of each tentacle-bulb is a single inclosed 

 lithocyst-cavity containing a spherical concretion. These 

 minute lithocysts lie buried in the ectoderm on the subumbrella 

 side of the bell a short distance above the insertion of the velum. 

 They are innervated by the inner nerve-ring (see Linko, 1900). 

 The mouth is an enormously elongated, cruciform slit 

 extending down the 4 radial-canals, almost to the bell-margin. 

 The radial-canals are thus converted into open gutters. The 

 edges of the radial-canals give rise to numerous, short, 

 branched, blindly ending diverticula, and the gonads are 

 developed in the ectoderm over these side branches and in the 

 walls of the cruciform lips. Hargitt, 1902, states that actinulae 

 develop upon the gonads. These lip-walls are short and their 

 free margins are crenated and folded in a curtain-like manner. 

 The entoderm of the radial-canals and circular canal is 

 milky-white, sometimes slightly yellowish or greenish. The 

 gelatinous substance of the bell is transparent and of a bluish 

 hue. As it floats languidly in the water the opaque entoderm 

 of the 4 canals presents the appearance of a large milky cross. 

 Young medusa. — In the youngest medusa observed, the 

 bell is hemispherical. There are 8 tentacles; 4 long radial 

 and 4 short interradial. Each tentacle-bulb is provided with a dark-colored ocellus upon 

 its inner side. There are 4 straight-edged, narrow, radial tubes. The manubrium is small 

 and has 4 simple lips. 



When the medusa is about 8 mm. in diameter (see vol. 1, plate 26, fig. 7), the tentacles 

 have increased in number and the manubrium has become much larger through the extension 

 of the 4 lips down the radial-canals, and the medusa begins to fulfil the conditions postulated 

 by Haeckel for " Staurostoma." 



When the animal is about 20 mm. in diameter (plate 26, fig- 4), the bell becomes quite flat 

 and the cruciform mouth has extended about half-way down the 4 radial-canals. In the 

 adult they finally reach the circular vessel and the radial-canals give rise to small, blindly 

 ending, lateral diverticula. 



This medusa is abundant north of Cape Cod, but is rarely seen except in early spring 

 upon the southern coast of New England. It makes its appearance in Massachusetts Bay 

 early in April, becomes mature in June, and disappears before the middle of July. At East- 

 port, Maine, however, they remain common until October. Mature individuals were found in 

 Newport Harbor, Rhode Island, from June 5 to 9, 1895. Hartlaub, 1897, has found this 

 species at Helgoland, and Wagner, Linko, and Birula have obtained it in the seas north of 

 Russia, and Levinsen records it from the coast of Greenland. It is evidently, therefore, an 

 Arctic species, and this fact, together with its similarity to Brandt's figures of Staurop/tora 



Fig. 



. — Staurophora mertensii. 

 Young medusa drawn by the 

 author, from specimen 25 

 mm. in diameter. Woods 

 Hole, Massachusetts. 



