320 MEIHTS.E OF THE WORLD. 



These medusae are probably derived from the Eucopidae through the multiplication of the 

 4 primitive radial-canals. In their youngest stages, indeed, the medusae of the ^Equondae 

 have only 4 radial-canals, but these increase by the growing outward of new canals from the 

 stomach-margin. Thus the medusa has at first 4, then 8, 16, 32, etc., radial-canals, although 

 this increase is usually irregular in its later stages. The medusae appear to develop through 

 alternations of generations from Campanularian hydroids, and asexual budding of daughter 

 medusae is unknown in the medusa stage of the iEquoridae. 



The medusae of the iEquoridae display a remarkable range of individual variability, both 

 of form and color— this being correlated with the multiplicity of their parts such as radial- 

 canals, tentacles, gonads, lithocysts, lips, etc. This high degree of variability has caused much 

 confusion in the synonymy, for "new species" have frequently been described from mere 

 growth-stages or varieties of one and the same medusa. This confusion is most noteworthy 

 in the genus ALquorea. 



The lithocysts in the ^Equoridae consist of closed velar vesicles containing concretions of 

 ectodermal origin. Excretory papillae are commonly seen upon the inner (subumbrella) side 

 of the ring-canal at the bases of the tentacles. 



Following is a synopsis of the genera of the yEquoridae: 



Octocanna Haeckel, 1879. 8 simple radial-canals, which arise separately from the periphery of the stomach. 8 lips. No ocelli. 



Octogonade Zoja, 1896. Similar to Octocanna, but the marginal sense-organs are provided with ocelli as well as with lithocysts. 



Stomobrachium Brandt, 1835 = Stomobrachium* Staurobrachium Haeckel, 1879. 8 or more simple radial-canals which arise 

 separately and at equal intervals from the periphery of the stomach. 4 lips. 



Halopsis A. Agassiz, 1863. Numerous radial-canals, which arise in 4 groups from the 4 perradial corners of the stomach. 4 lips. 



Equorea Peron and Lesueur, iScx) = &<]uorea+ Rhegmatodes + Mesonema+ Polycanna Haeckel, 1879. More than 8 simple 

 radial-canals which arise separately from the periphery of the stomach. More than 4 lips. Subumbrella smooth without 

 gelatinous protuberances. Hydroid is Campanulina. 



Zygodactyla Brandt, 1835; wish Agassiz, 1862. Similar to Mquorea, but with interradial rows of wart-like protuberances upon 

 the floor of the subumbrella. . 



Zygocanna=Zygocanna + Zygocannota Haeckel, 1879- With bifurcated or branched radial-canals which arise at equal inter- 

 vals from the periphery of the stomach. The stomach lacks a peduncle. More than 4 lips. 



Zygocannula Haeckel, 1879. Similar to Zygocanna, but the stomach is mounted upon a gelatinous peduncle. 



Genus OCTOCANNA Haeckel, 1879. 



Octocanna, Haeckel, 1879, Syst. der Medusen, p. 213— Maas, 1905, Craspedoten Medusen der Siboga Expedition, Monog. 10. 

 p. 38; Revue Suisse de Zool., tome 14, p. 94.— Browne, 1905, Report on Pearl Oyster Fisheries, Gulf of Manaar, Roy, 

 Soc. London, Suppl. Report No. 27, p. 145.— Bigelow, 1909, Mem. Museum Comp. Zool. at Harvard College, vol. 37, 

 p. 168. 



Haeckel establishes this genus for two medusae, the first one being called Octocanna 

 octonema and the second 0. polynema. 0. octonema is probably the young of O. polynema 

 and the type species becomes 0. polynema of the Indian Ocean. Haeckel states that there are 

 4 lips, but the recent researches of Maas and Browne show that there are 8 lips. 



GENERIC CHARACTERS. 



iEquoridae with 8 simple radial-canals, which arise separately, 45 apart, from the 

 periphery of the stomach. 8 lips. Lithocysts without ocelli. Manubrium without a peduncle. 



This genus bears a close resemblance to Octogonade Zoja, 1896, but in Octogonade the 

 marginal sense-organs are provided with ocelli as in Tiaropsis, whereas in Octocanna there are 

 no ocelli. 



All species of Mquorea pass through an "Octocanna stage" in their ontogeny, and indeed 

 Octocanna may be regarded as only a special form of Mquorea, which becomes mature with 8 

 radial-canals. 



Octocanna polynema Haeckel. 



Octocanna polynema, Haeckel, 1879, s vst- der Medusen, p. 214.— Browne, 1905, Report on Pearl Oyster Fisheries, Gulf of 

 Manaar, Supplementary Report 27, Roy. Soc. London, p. 144, plate 2, figs. 8-10— Maas, 1905, Craspedoten Medusen 

 der Siboga Expedition, Monog. 10, p. 38; 1906, Revue Suisse de Zool., tome 14, p. 95, plate 3, fig. 10.— ( ?)Bigelow, 

 H. B., 1909, Mem. Museum Comp. Zool. at Harvard College, vol. 37, p. 169, plates 6 and 38. 



Bell about 12 to 25 mm. wide and 4 to 6 mm. high, with thick, gelatinous walls. 32 to 

 80 filiform tentacles with swollen basal bulbs; the tentacles are about half as long as bell-radius. 

 The bulbs have well-developed, excretory papillae. There are no cirri nor rudimentary tentacle- 



