244 MEDUSAE OF THE WORLD. 



Obelia gymnophthalma Spagnolini, 1876 (Catalogo Acalefi Mediterraneo, p. 31, tav. 6, 

 figs. 1, 2), from Naples, is probably an Obelia with a Sagitta held in its mouth, thus giving the 

 appearance of a long conical manubrium. 



Billard, 1901 (Comptes Rendus, Paris, p. 441), shows that hydroids of Obelia such as 

 0. geniculata and 0. flabellata, often reproduce by scissiparity. That is to say portions of 

 thehydroid stems break off and after falling to the bottom reproduce new stocks. 



Obelia gelatinosa Hincks. 



Sertularia gelatinosa, Houttuyn, 1761-73, Natuurlyke historie Dieren, Planten en Mineralien, Amsterdam, vol. 17, p. 564 — 

 Pallas, 1766, Elenchus Zoophytorum, p. 116. 



Non Campanularia gelatinosa, Van Beneden, 1844, Nouv. Mem. Acad. Bruxelles, tome 17, p. 33, plates 1, 2. This is probably 

 Obelia longissima ( ?): 



Obelia dichotoma, Allman, 1864, Annals and Mag. Nat. Hist., vol. 13, p. 372. 



Laomedea gigantea, Agassiz, A., 1865, North American Acal., p. 94. 



Obelia gelatinosa, Hincks, 1868, British Zoophytes, p. 151, plate 26, fig. 1— Graeffe, 1884, Arbeit. Zool. Inst. Wien, Bd. 5, 

 p. 356.— Bedot, 1901, Revue Suisse de Zool., tome 9, p. 430; 1905, tome 13, p. 50 (citation of literature to 1850).— 

 Nutting, 1901, Bull. U. S. Fish Commission, vol. 19, p. 351, figs. 39, 39A.— Hargitt, 1904, Bull. U. S. Bureau of 

 Fisheries, vol. 24, p. 48.— Rufford (edited by E. Connold), 1902, Notes on British Zoophytes, p. 57, plate 2, fig. 3. 



Obelia leucostyla, Will, 1844, Horae Tergestina;, p. 73, taf. 2, fign. 16-19. 



Obelia leucostyla+ 0. gelatinosa, Haeckel, 1879, Svst - der Medusen, pp. 174, 176, taf. 11, fign. 6, 7. 



The hydroid forms a large compound cluster of relatively straight, tapering main stems 

 which arise from a fibrous, spongy hydrorhiza. The main stems ioo to 250 mm. high, tree- 

 like, dark-brown in color, and thickly branched. The branches are given off in pairs at short 

 intervals and placed alternately on opposite aspects of stem, so as to present a subverticillate 

 arrangement. The main stem and basal parts of the branches are composed of numerous, 

 delicate tubes closely bound together and tapering upwards. The primary branches branch, 

 as does main stem, into numerous, alternate ramules, annulated with 2 to 4 rings above the 

 divisions. Hydrothecae very small, thin-walled, smooth, and conical, and often borne upon 

 long, tapering pedicels ringed at both ends. The margin of the hydrotheca is cut into deep 

 denticles of a castellated form slightly hollowed at top (see Hincks). The polypites have about 

 24 tentacles. Gonothecx small, ovate to club-shaped, widest near upper end, and with a 

 flattened top and raised, crater-like aperture. They arise from the axils of the stem and are 

 supported upon short pedicels having several rings. Each gonangium contains several 

 medusa-buds. The main stems are horny, dark-brown and the finer and ultimate branches 

 are pellucid white. 



When set free the medusae usually have 16 tentacles and the gonads are already beginning 

 to migrate down the radial-canals from the sides of the manubrium. 



This hydroid is exceedingly abundant upon seaweeds in shallow water along the Atlantic 

 and Mediterranean coasts of Europe, and in America from Cape Cod to the Carolinas. Graeffe 

 states that the hydroid is found at Trieste, Adriatic, upon mussels, and that the medusa; appear 

 in March. It is a common hydroid on the southern coast of New England, United States, 

 and is often found in shaded places attached to the wooden piling of docks, where its large, 

 tree-like tufts are very conspicuous. 



Obelia commissuralis McCrady. 



( >) Campanularia geniculata, Van Beneden, 1844, Mem. Acad. Roy. de Bruxelles, tome 17, p. 34, plate 3, figs. 1-6. 



Obelia commissuralis, McCrady, 1857, Gymn. Charleston Harbor, p. 95, plate 1 1, figs. 5-7— Agassiz, L., 1862, Cont. Nat. 

 Hist. U. S., vol. 4, pp.315, 351, plate 33 (non fig. 2), plate 34, figs. 10-21 —Agassiz, A., 1862, Proc. Boston Soc. Nat. 

 Hist., vol. 9, p. 91, fig. 5; 1865, North Amer. Acal., p. 91, figs. 134, 135— Haeckel, 1879, Syst. der Medusen, p. 174 — 

 Brooks, 1882, Studies'Biol. Lab. Johns Hopkins Univ., vol. 2, p. 136.— Nutting, 1901, Bull. U. S. Fish Commission, 

 vol. 19, pp. 350, 380, figs. 36, 97.— Torrey, 1902, California University Publications, Zool., vol. 1, p. 56.— Hargitt, 

 1904, Bull. U. S. Bureau of Fisheries, vol. 24, p. 48. 



Laomedea gelatinosa, Stimpson (non Auct.), 1853, Marine Invert. Grand Manan, p. 8. 



Laomedia gelatinosa, Gould, 1841, Report Invert. Animals Mass. Bay, p. 350. 



Laomedea dichotoma, Leidy, 1855, Marine Invert. N. J. and R. I., p. 6, plate 9, fig. 36. 



(>)Obelia commissuralis, Verrill, 1873, Report Commiss. Fish and Fisheries U. S., for 1871-72, p. 728, plate 37, fig. 281. 



Hydroid and young medusa. — This species is found attached to stones and seaweed near 

 low-water mark. The" stems of the hydroid are tree-like and are often 125 to 150 mm. in 

 length, although medusae are often given off from stocks of only 25 mm. in height. The stock 

 usually consists of a long main stem that branches but little, and the side branches spring out 



