LEPTOMEDUS.E — OBELTA. 249 



Obelia plana Haeckel. 



Thaumantias plana, Sars, 1835, Beskriv og Jagttagelser, Bergen, p. 28, plate 5, figs. 13 a-g. 



Campanularia flabellata, Hincks, 1866, Annals and Mag. Nat. Hist., vol. 18, p. 297. 



Obelia fabellata, Hincks, 1868, Hist. British Hydroid Zooph., p. 357, plate 29, 3 figs.— Nutting, 1901, Bulletin U. S. Fish Com- 

 mission for 1899, pp. 358, 380, fig. 35. — Melley, Hincks and Herdmann, 1886, Hydroids L. M. B. District, p. 102.— 

 Haroitt, 1908, Biol. Bulletin, vol. 14, p. 109, fig. 12 (medusa).— Billard, 1901, Compt. Rend. Paris, tome 133, P-44I. 



Obelia plana, Haeckel, 1879, Syst. der Medusen, p. 177.— Bedot, 1905, Revue Suisse de Zool., tome 13, p. 140; Ibid., tome 

 13, p. 95 (literature 1835-1850). 



The main stems are about 200 mm. high, filiform, somewhat zigzag, and strongly annu- 

 lated with about 2 to 5 rings above the points of origin of the branches. Main stem dark horny- 

 brown color. Branches alternate, fairly short and fan-shaped, more or less dichotomous in 

 their manner of ultimate branching, and ringed above each division. They generally fork 

 immediately beyond point of origin, and arms of fork trend in opposite directions, thus giving 

 a subverticulate appearance to the ramification. 



The hydrothecas are alternate, short, widely flaring, and conical, with simple, entire mar- 

 gins. They are borne on completely ringed and tapering pedicels of variable length, some 

 being short, others long, and having a range of about 3 to 10 rings. 



The reproductive calycles arise from the axils of the stems and are ovate to club-shaped, 

 somewhat flattened at outer end, and with a short tubular orifice. They are attached by short 

 ringed stalks. (See text-figure 130. ) 



Found in rocky tide-pools on the British and Norwegian coasts, and identified by Nutting 

 from depths of 4 to 5 fathoms near Woods Hole, Massachusetts, and in Long Island Sound. 



According to Hargitt the medusa which is liberated by 0. flabellata Hincks is at liberation 

 0.4 to 0.5 mm. in diameter, and has 24 tentacles, 8 adradial concretions, and 4 well-developed 

 oval gonads near the middle of its radial-canals. Billard found that the hydroid often breaks 

 into pieces and these upon anchoring themselves develop into new stocks. 



Obelia borealis Nutting. 

 Obelia borealis, Nutting, 1901, Proc. Washington Acad. Sci., vol. 3, p. 174, plate 19, figs. 4, 6. 



Trophosome. — Colony sometimes attaining a height of 440 mm., usually much shorter; 

 stem not truly fascicled, although several stems may be interwoven, exceedingly long and 

 slender, sinuous, giving off lateral branches in pairs on proximal part and more often singly 

 on distal part; branches with a strong tendency to verticillate arrangement, forming oblique 

 angles with the stem and divided into numerous branchlets in a flabellate manner. Pedicels 

 short and completely annulated, or long and annulated only at ends, set on broad shoulders 

 of the stem. Hydrothecae funnel-shaped, sides usually straight, aperture with an even rim. 

 Hydranths not well preserved in specimens examined. 



Gonosome. — Gonangia borne in axils of branches and branchlets, oblong-ovate, truncated 

 above, having a collar in mature specimens; aperture apparently very large, pedicels strongly 

 annulated. The gonangia of the specimens examined were filled with developing medusae of 

 the regular Obelia type. 



Found at Yakutat, Alaska (Harriman Expedition). 



This species is related to 0. flabellata, but the hydrothecae are much deeper than in 

 0. flabellata, in which they are subtriangular in outline. It also bears some resemblance 

 to 0. commissuralis, which, however, is a much more delicate species, with smaller and more 

 campanulate hydrothecae. 



Obelia geniculata Allman. 



Sertularia geniculata, Linne, 1758, Systema Naturae, ed. 10, p. 812; 1761, Fauna Suecica, p. 541; 1767, Syst. Naturae'tome 1, 



Pars 2, p. 13 1 2. 

 Campanularia geniculata, Meyen, 1834, Acta Acad. Caes. Leop. Carol., Nat. Cur., tome 16, Suppl., p. 319, tab. 41, figs. 3-5. 

 Laomedia geniculata, Johnston, 1838, History of British Zoophytes, p. 151, plate 21, figs. I, 2. 

 Eucope diaphana, Agassiz, L., 1862, Cont. Nat. Hist. U. S., vol. 4, pp. 322, 352, plate 34, figs. 1-90. 

 Eucope alternata, Agassiz, A., 1865, North Amer. Acal., p. 86. 

 Obelia geniculata, Allman, 1864, Annal. and Mag. Nat. Hist., ser. 3, vol. 13, p. 372; 1871, Monog. Tubularian Hydroids, p. 141, 



fig. 59.— Hincks, 1868, History of British Zoophytes, p. 149, plate 25, figs. 1, la.— Verrill, 1873, Report of Commiss. 



Fish and Fisheries, U. S. A., for 1871-72, p. 727. 

 Obelia diaphana+O. lucifera ( ?), Haeckel, 1879, Svst - aer Medusen, p. 175. 



