48 



BULLETIN <>F THE BUREAU < >F FISHERIES. 



Obelia diaphana. 



Obelia commissuralis McCrady. 



Laomedia gelatinosa Stimpson, Marine Invertebrates of Grand Manan, 1853, p. 8, in Smithsonian Contributions to Knowl- 

 edge, Vol. VI. 



Laomedia dichotoma Leidy, Marine Invertebrates of New Jersey and Rhode Island, 1*«, p. 6. in Journal Academy Natural 

 Sciences of Philadelphia, Vol. Ill, 2d series. 



Obelia commissuralis McCrady, Proceedings Elliott Society of Natural History. Vol. 1, 1857, i>. 197. L. Agassiz, Contributions 

 to Natural History of United States. Vol. IV. 1862, pp. 315, 851. A. Agassiz, North American Acalephse; 1865, p. 91, 

 in Bulletin Museum Comparative Zoology, Vol. I. Haeckel, System der Medusen, 1879, p. 174. 



Bell flat and discoid; mar- 

 ginal tentacles Hi at liberation; 

 gonads borne on distal half of 

 radial canals; manubrium cylin- 

 drical, mouth four-lobed. Size 

 <>f medusa about 1 mm. at time 

 of liberation. Developed from 

 hydroid of same name. 



Distribution. — Everywhere 

 throughout the region. Hydroid 

 found en various specit-s of TPueus, and very 

 polific, hundreds of medusae being discharged 

 from a small colony within a few hours at the 

 breeding season. 



Obelia diaphana ( L. Agassiz. I Text cuts. 



Thaumantias diaphana I.. Agassiz, Memoirs American 

 Academy of Arts and Sciences, Vol. IV. 1843, 

 p. 300. 



Eneope diaphana A. Agassiz, in L. Agassiz, Contributions 

 to Natural History of United Stall's, Vol. IV, 

 1862, p. 322. North American Acalephse, 1865, 

 p. 83. 



Obelia diaphana Allman, Annals and Magazine of Nat- 

 ural History, Vol. XIII, 1864, p.372. Haeckel, 



System tier Medusen, 1ST'.', p. 175. 



Medusa flat, discoid, with usually L'4 ten- 

 tacles at liberation, later as many as 200 or 

 more. Size about 1 mm. at birth, becoming 

 as much as 5-6 mm. at maturity. Manubrium 

 cylindrical, with four-lipped mouth, lipsshort. 

 Gonads usually absent at birth, becoming 

 pyriform at maturity, and borne on distal third 

 of radial canals. 



Development as in preceding species, the young sometimes occurring in almost incredible iitiiii- 

 hers. Hydroid stock very similar to preceding species. 



Distribution as id' preceding. Common everywhere. 



Obelia gelatinosa (Pallas). 



Serluiaria gelatinosa Pallas, Elenchus Zoophytorum, 1766, p. 116. 



Laomedia gelatinosa Lamarck. Animaux sans Vertebres. Tome II, 1817, p. 134. Lamouroux, Histoire des Polypiers 



Coralligenes Flexible. 1816, p. 92. 

 Laomedia gigantea A. Agassiz, North American Acalephse, 1865, p. 94. 

 Obelia gelatinosa Haeckel. System der Medusen, 1879, p. 176. 

 til; I hi dichotoma Allman. Annals and Magazine of Natural History, Vol. Nil I. lstil. p. 372. 



Medusa much as preceding as to general form, tentacles, etc Tentacles at birth It; (Hincks), 24 

 (Haeckel). Manubrium and gonads about as in preceding species. Development from hydroid 

 stock of same name, which, in contrast to those of both the previous species, is very large, attaining 

 a height of a foot or more. 



Distribution. — Less common than preceding, though taken throughout region. 



Obelia diaphana 



