238 MEDUSA OF THE WORLD. 



Eucope parvigastra. 



Plate 31, fig. 5. 

 Eucopium parvigastrum, Mayer, 1900, Bull. Museum Comp. Zool. at Harvard College, vol. 37, p. 52, plate 42, fig. 140. 



Bell half-egg-shaped, I mm. high, with small, dome-like, apical projection. 4 small, 

 radially situated tentacles, hardly more than mere tentacle-bulbs. 8 lithocysts, 2 in each quad- 

 rant, each containing a single spherical concretion. Velum well developed. 4 straight, narrow 

 radial-canals and a slender circular vessel. Manubrium very small, a mere tube, cruciform in 

 cross-section, and provided with 4 simple lips. The gonads occupy 4 linear swollen regions 

 near the middle of the 4 radial-canals. Entoderm of tentacle-bulbs, gonads, and manubrium 

 of a decided brown color. 



This medusa was quite common at Tortugas, Florida, late in June, 1899. It is distin- 

 guished from other species of Eucope by its very small manubrium, and in this respect it appears 

 to foreshadow the condition seen in Agastra, wherein manubrium has entirely disappeared. 

 Development unknown. 



Genus OBELIA Pe'ron and Lesueur, 1809. 



Medusa marina, Slabber, 1781, Physikalischen Belustigungen, p. 40, taf. 9, fign. 5-8. 



Obelia, Peron et Lesueur, 1809, Tableau des Meduses, etc., Ann. Mus. Hist. Nat. Paris, tome 14, p. 355. — McCrady. 1857, 

 Gymn. Charleston Harbor, p. 94. — Allman, 1864, Ann. and Mag. Nat. Hist., ser. 3, vol. 13, p. 372. — Hincks, 1868, 

 British Hydroid Zoophytes, p. 146. — Kowalevsky, 1873, Mejn. Imp. Soc. Friends of Nat. Hist., vol. 10, Part 2, Moscow 

 (development). — Haeckel, 1879, Syst. der Medusen, p. 171. — Hartlaub, 1894, Ccelenteraten Helgolands, p. 171. — Nut- 

 ting, 1901, Bull. U. S. Fish Commission, vol. 19, p. 349; Proc. Washington Acad. Sci., vol. 3, p. 173. — Hartlaub, 

 1905, Zoolog. Jahrbuchern, Suppl. p. 580. — Bedot, 1901, Revue Suisse de Zool., tome 9, p. 457; Ibid., tome 13, p. 95 

 (list of papers). 



Laomedea, Lamouroux, 1812, Nouv. Bull. Sci. Soc. Philomantique, tome 3, p. 184, Paris. 



Obelia, de Blainville, 1834, Manuel d'Actinologie, p. 281, Paris. 



Thaumantiai (in part), Forbes, 1848, British Naked-eyed Medusa?, p. 41. 



Eucope (in part), Gegenbaur, 1856, Zeit. fur wissen. Zool., Bd. 8, Heft 2, p. 241. 



Obelia+ Eucope, Agassiz, L., 1 862, Cont. Nat. Hist. U.S., vol. 4, p. 351 . — Agassiz, A., 1865, North American Acalepha?, pp. 83, 91 . 



Obelia+Schhocladium, Allman, 1871, Browne, E. T., 1906, Quart. Journ. Microscop. Sci., vol. 50, p. 645; Allman, Ibid., 

 1871, vol. 11, p. 18. 



Eucope, Agassiz and Woodworth, 1896, Bull. Museum Comp. Zool. at Harvard College, vol. 30, p. 121. 



The genus Obelia was founded by Peron and Lesueur, 1809, for a form which had been 

 described by Slabber under the name of Medusa marina. This medusa conforms in all respects 

 to the characters of the genus Obelia as we here define it. The genus Thaumantias as defined 

 by Forbes, 1848, includes Phialidium as well as Obelia, and this is true also of Eucope as 

 defined by Gegenbaur, 1856. The name " Obelia" was restored by McCrady, 1857, for Obelia 

 commissurahs. 



GENERIC CHARACTERS. 



Eucopidae with numerous tentacles. The 4 sac-like gonads are upon the 4 radial-canals. 

 There is no peduncle. Tentacles peculiar in that their axial entoderm projects inward from 

 margin into the gelatinous substance of the bell. The 8 vesicular, adradial lithocysts are 

 borne upon under side of basal bulbs of 8 of the tentacles. 



This genus is readily distinguished from Phialidium and from Clytia by the fact that in 

 Obelia there are but 8 lithocysts, 2 in each quadrant. Moreover, in Obelia the tentacle-bulbs 

 project inward into the gelatinous substance of the bell, whereas in Clytia and Phialidium 

 this is not the case. 



Obelia is also distinguished from Tiaropsis L. Agassiz by the absence of marginal eye- 

 spots and by its simple, closed lithocysts. The lithocysts in Obelia usually contain a single 

 concretion instead of many, as in Tiaropsis. It is distinguished from Eucheilota by the absence 

 of lateral cirri at the sides of the tentacles, and from both by its inwardly projecting tentacle- 

 cores. 



Mature medusae of Obelia, all possessing 8 marginal lithocysts and a large and variable 

 number of tentacles, are exceedingly common along the New England coast from April until 

 the last week of November. Owing to the similarity in size and appearance of the mature 

 medusae, one would be led to believe that they all belonged to one and the same species. Upon 

 examination of the hydroid stocks, however, differences that may be of specific value are 



