TRACHYMEDUSiE SMINTHEA, HOMCEONEMA. 



383 



Sminthea eurygaster Gegenbaur. 



Sminthea eurygaster, Gegenbaur, 1856, Zcit. fur wissen. Zool., Bd. 8, p. 245, taf. 9, fign. 14-15. — Metschnikoff, E., 1886, 



Arbeit. Zool. Inst. Wien, p. 244. 

 Tholus eurygaster, Agassiz, L., 1862, Cont. Nat. Hist. U. S., vol. 4, p. 365. 

 Trachynema eurygaster, Haeckel, 1879, Syst. der Medusen, p. 260. — Maas, 1893, Ergeb. dcr Plankton Exped., Bd. 2, K.c., 



p. 12. — Browne, 1906, Trans. Linnean Soc. London, ser. 2, Zool., vol. 10, p. 171. 

 Marmanema mammtcjorme, Haeckel, 1879, Syst. der Medusen, p. 262. 



This is a rare medusa. Bell 4.5 mm. wide and 2 mm. high. 8 radially placed tentacles 

 and 8 interradial lithocysts. Velum about half as wide as bell-height. Manubrium only about 

 one-fourth to one-half as long as depth of bell-cavity. 8 gonads, small, globular to egg-shaped, 



226. 



226. 



229. 



227. 22 8- 



Fig. 226— Sminthea eurygaster, after Gegenbaur, inZeit.fiirwissen.Zool.,Bd.8. Side view of medusa and enlarged view of gonad. 



Fig. 227. — "Marmanema mammsforme," after Haeckel, 1879.= Sminthea eurygaster. 



Fig. 228.— "Sminthea leptogaster," after Gegenbaur, in Zeit. fur wissen. Zool., Bd. 8.= Rhopalonema velatum (?) 



Fig. 229.— "Trachynema longivenlris," after Maas, in Ergeb. Plankton Expedition. Young stage of H. typicum ? 



project from the 8 radial-canals very near the ring-canal. Medusa with tentacle-bases faint 

 red, gonads faintly yellow. Found in the Mediterranean and in warm parts of the Atlantic. 

 It is distinguished by its protrusive, sac-like gonads, close to the bell-margin and by having 

 but 8 tentacles when mature. 



Genus HOMCEONEMA Maas, 1893, 1897. 

 Trachynema+ Homceonema, Maas, 1893, Ergebnisse der Plankton Exped., Bd. 2, K.c, pp. 12, 15, 20. 

 Homaonema, Maas, 1897, Mem. Mus. Comp. Zool. at Harvard College, vol. 21, p. 22. 

 Cohbonema+ Homuonema, Vanhoffen, 1902, Wissen. Ergeb. deutsch. Tiefsee Exped., Dampfer Vaidivia, Bd. 3, Lfg. 1, pp. 



56, 62. 

 Isonema (in part), Maas, 1906, Expedition Antarctique, S.Y. Belgica, p. 4, Anvers. 

 Colobanema, Bigelow, H. B., 1909, Mem. Mus. Comp.Zool. at Harvard College, vol. 37, p. 132. 



Maas founded this genus in 1893 for two medusae, the first to be described being Homce- 

 onema platygonon of the north Atlantic. 



GENERIC CHARACTERS. 



Medusa similar to Rhopalonema, but the tentacles are all similar in structure each to 

 each. 4 lips. 8 radial-canals with 8 localized gonads. No peduncle. Tentacles arising in a 

 single row from the bell-margin. 



In 1902 Vanhoffen established the genus Colobonema for a medusa which may have been 

 described by Maas, 1897, under the name Homceonema typicum. Vanhoffen discovered that 

 in this medusa the 8 tentacles which are midway between the 8 radial-canals are the last to 

 develop. Thus the medusa may have 24 well-developed tentacles and 8 young (small) inter- 

 radial tentacles, 32 in all. In other respects this medusa is similar to Homceonema, and indeed 

 I regard it as a special case of Homceonema in which the interradial tentacles are the last to 

 appear. 



Bigelow, 1909, calls attention to the fact that no one has seen lithocysts in "Colobonema 

 sericcum," but we must remember that these bodies are very readily lost in Trachymedusae. 



