254 MEDl'S.K OF THE WORLD. 



Found by Hartlaub at great depths off Helgoland, German Ocean. Medusae are found 

 late in September. 



Obelia adelungi Hartlaub. 



Obelia adelungi, Hartlaub, 1884, Zeit. fur wissen. Zoo]., Bd. 41, p. 164, text-fig. 1, taf. u.fign. 1, 2, 5, etc.; taf. 12, fig. 31; 

 1894, Wissen. Meeresuntersuch. Kommis., Meere Kiel, Helgoland, ser. 2, Bd. I, p. 173. 



Medusa flat, shield-shaped, about 2.5 mm. wide. 24 tentacles, which are not quite half as 

 long as bell-radius. Manubrium less than one-third as long as bell-radius; cylindrical, with 

 4 lips. 4 gonads on outer thirds of the 4 radial-canals, but not extending to ring-canal. When 

 set free there are no gonads upon the radial-canals. Colorless. 



The hydroid is flense, tree-like, and thick-stemmed; brown in color and about 80 to 100 

 mm. high. The branches arise on alternate sides of the main stem from the ground upward. 

 The branching of the side branches is, however, quite irregular, but profuse. Hydrothecae 

 about 0.5 mm. long, with simple entire edges, without notches on margin. The pedicels of 

 the hydrothecje are about 0.8 mm. long and usually ringed throughout. Gonangia elongate, 

 conical, and mounted upon very short pedicels. They are developed at the axils between 

 branches, and most of them are near the base of the stock. 



Found late in September at Helgoland, German Ocean, at great depths. 



Hartlaub showed that in this medusa and in Obelia helgolandica the germ-cells begin to 

 develop upon the second day after the medusa has been liberated from trje hydroid. The 

 germ-cells originate in the ectoderm upon the 4 upper, interradial sides of the manubrium, and 

 only later do they migrate into their final position over the radial-canals. After the eggs have 

 begun to differentiate in the ectoderm of the manubrium, some of them migrate through the 

 basement membrane and enter the entoderm. When the medusa is mature, the greater 

 number of the young eggs in the gonad are found in the entoderm, but later a number of 

 them migrate into the ectoderm, where they mature. The sperm-cells originate in the ecto- 

 derm and migrate into the spermaries, where they remain in the ectoderm. 



Hartlaub states that this medusa is quite different from 0. gelatinosa. 



Obelia bidentata Clarke. 



Obelia bicuspidata-^ . bidentata, Clarke, 1875, Transactions Connecticut Acad. Sci., vol. 3, p. 58, plate 9, fig. 2. 

 Obelia bidentata, var., Pictet, 1893, Revue Suisse de Zoologie, tome 1, p. 25, plate 1, figs. 20, 21 (from Amboina). 

 Obelia bidentata, Marktanner-Turneretscher, 1890, Ann. naturh., Hofmus. Wien, Bd. 5 (from the Arru Islands). 

 {Obelia bicuspidata= Obelia bidentata) >, Nutting, 1901, Bull. U. S. Fish Commission for 1899, p. 351. 

 (?) Obelia austro-georgia, Jaderholm, 1904, Archiv. Zool. Exper., ser 4, tome 3, p. vii. 



O. bidentata and 0. bicuspidata of Clarke are probably one and the same species, for 

 Nutting found an intergrading form between the two. In 0. bicuspidata the colony is about 

 80 mm. high, with straight, irregularly branched main stems. Pedicels of the hydrothecae have 

 10 to 15 annulations. The hydrothecae are very deep and tubular, with margins armed with 

 bimucronate teeth, between which lines originate which pass longitudinally down the surface 

 of the hydrotheca. 



0. bidentata resembles O. bicuspidata, but attains a larger size, has shorter pedicels with 

 only 4 to 6 annulations, and proportionately wider hydrothecae. Nutting suspects that the 

 two "species" are but extreme forms of an intergrading series. 



No gonosome known. Medusa unknown. Found by Clarke and Nutting in or near 

 Long Island Sound, Atlantic coast of southern New England; and by Pictet and Marktanner- 

 Turneretscher in the Malay Archipelago, at Amboina, and the Arru Islands. 



This species is distinguished by its long subcylindrical hydrothecae with their longitudinal 

 ridges and strongly dentate margin. 



Obelia? bifurca Hincks, 1887, Journ. Linnean Soc. London, vol. 21, p. 133, plate 12, 

 fig. 1, resembles O. bicuspidata Clarke, but is stouter and longer. The calycles are very slender 

 and lineated longitudinally with 8 to 10 lines, extending from the rim nearly to base. 

 Pedicels are long and taper upwardly, and the stem is compound. The rim is cut into about 

 12 broad bicuspid denticles. Found on N cilia oculata at the Mergui Archipelago oft the 

 coast of Tenasserim. 



