376 MEDUSA OF THK WORLD. 



Family TRACHYNEMID^ Gegenbaur 1856. 



Trachvnemidie, Gegenbaur, 1856, Zeit. fiir wissen. Zool., Bd. 8, p. 218. 

 Trachynemidai+ Aglauridte, Haeckel, 1879, Syst. der Medusen, pp. 255, 268. 



FAMILY CHARACTERS. 



Trachymedusae with 8 or more simple radial-canals, on some or all of which the gonads 

 are developed. No mesenterial partitions in the subumbrella. Tentacles without adhesive 

 disks. Ring-canal simple and without centripetal branches. 



We may distinguish two subfamilies: (i) Rhopaloneminae, in which the stomach lacks a 

 peduncle; and (2) Aglaurinae, in which the stomach is mounted upon a gelatinous peduncle. 

 The genera are as follows: 



Subfamily Rhopaloneminse: Trachynemida: in which the stomach lacks a peduncle. 



Rhopalonema Gegenbaur, 1856= Trachynema (young medusa, Gegenbaur, 1854)= Trachynema^ Rhopalonema + Marmantma 

 Haeckel, 1879. With 8 well-developed, radial tentacles and 8 or more small, cirrus-likeorclub-shaped,interradial tentacles. 

 All tentacles arise in a single row. 8 gonads localized on the 8 radial-canals. 4 lips. 



Smitilhea Gegenbaur, 1856. Similar to Rhopalonema, but with only 8 tentacles, one at foot of each of the 8 radial-canals. 



Homceonema Maas, 1893= Colobonema Vanhofeen, 1 902= .Tsonfma (in part) Maas, 1906. Similar to Rhopalonema, but the 

 tentacles are all of one sort. No small, club-shaped or cirrus-like tentacles. 4 lips. 



Tetrorchis Bigelow, H. B., 1909. 8 radial-canals, 4 gonads, 4 lips. 



Pantachogon Maas, 1893. Gonads not localized as in Homceonema and Rhopalontma, but diffusely developed over the radial- 

 canals. 4 lips. 



Halicreas Fewkes, 1882 = Halicreas + Haliscera Vanhofeen, 1902= Isonema (in part) Maas, 1906. The mouth is a simple 

 round opening without 4 lips. (In all known species the radial-canals and ring-canal are very broad and flat.) Wart-like 

 protuberances may be present upon the sides of the exumbrella. Radial tentacles large; interradial, small. Tentacles 

 arise in a single row. Each tentacle terminates in a stiff, bristle-like outer end. 



Halitrephes Bigelow, H. B., 1909. Similar to Halicreai but with more than 8 radial-canals, 



Botrvnema Browne, 1908. Similar to Halicreas, but the tentacles are grouped into clusters; the tentacles of each cluster 

 arise in a single linear row from the bell-margin. 



Crossoia Vanhofeen, 1902. The tentacles arise in several rows from the bell-margin. Mouth with 4 lips. 



Subfamily Aglaurina;: Trachynemida in which the stomach is mounted upon a peduncle. 



Asjaura Peron and Lesueur, 1809. 8 gonads on peduncle above stomach. Sexes separate. Development direct. 

 Aglantha= Aglantha + Agiscra Haeckel, 1879. 8 gonads on subumbrella, or at turning-points of the 8 radial-canals between 



the peduncle and the subumbrella. Sexes separate. 

 Amphogona Browne, 1904. Similar to Aglantha, but the medusa may be bisexual, 4 of the gonads being male and 4 female. 

 Siauraglaura Haeckel, 1879. 4 gonads, one upon each alternate radial-canal. 

 Persa McCradv, 1857. 2 gonads on 2 of the radial-canals 180 apart. The 6 other radial-canals are sterile. 



Subfamily RHOPALONEMINiE. 



Genus RHOPALONEMA Gegenbaur, 1856. 



Trachynema, Gegenbaur, 1854, Zur Lehrc Generationswechsel Medusen, Wurzburg, p. 53 (young medusa without gonads). 

 Trachynema-^- Rhopalonema, Gegenbaur, 1856, Zeit. fiir wissen. Zool., Bd. 8, pp. 245-251. 

 Calyptra, Leuckart, 1856, Archiv. fiir Naturgesch., Jahrg. 22, p. 14. 



Trachynema (in part)+ Marmanema+ Rhopalonema, Haeckel, 1879, Syst. der Medusen, pp. 259-264. 

 Trachynema + Rhopalonema, Maas, 1893, Ergebnisse der Plankton Exped., Bd. 2, K. c, pp. 12-18. 

 Rhopalonema, Vanhoffen, 1902, Wissen. Ergeb. Deutsch. Tiefsee Expedition, Dampfer Valdivia, Bd. 3, Lfg. I, p. 59. 

 Rhopalonema, Maas, 1904, Result. Camp. Sci. Prince de Monaco, fasc. 28, p. 27.— Bigelow, 1909, Mem. Mus. Comp. Zool. at 

 Harvard College, vol. 37, p. 127. 



The type species is Rhopalonema velatum Gegenbaur, 1856. The young of this species 

 was probably described by Gegenbaur in 1854 under the name Trachynema ciliatum. This 

 medusa is distributed throughout the tropical and warm oceans of the world, but Gegenbaur 

 described it from the Mediterranean. 



GENERIC CHARACTERS. 



Trachymedusae, with 8 well-developed, radially placed tentacles and 8 or more club- 

 shaped or cirrus-like tentacles which arise from the bell-margin between the radial-canals. 

 All of the tentacles arise in a single row from the bell-margin. The 8 gonads occur upon 

 restricted portions of the 8 radial-canals. 4 lips. Stomach without a peduncle. Lithocysts 

 inclosed. 



Haeckel, 1879, distinguishes three genera in a sense equivalent to our Rhopalonema, thus: 

 Trachynema, with 4 lithocysts, M armanema with 8, Rhopalonema with 16. 



