52 CAIIPANELLA PACHYDERMIA. 



Avitli the two species of Tracliynema here enumerated, I am inchned to 

 add, near this suborder, two other famihes, the position of which in the 

 different systems of classification has always been a great puzzle. I 

 mean the Trachynemidaj and the Ger3^onidjB (Persa, Aglaurida;).* The 

 peculiar solid character of the bell of these families, incapable of con- 

 traction to any extent, is in striking contrast with the tran.sparent i\\my 

 disk of the true Hydroids, reminding us of the solid mass of the larger 

 Discophora?. The character of the development, also, which takes 

 place directly from the egg. differs from that of the true Hydroids, 

 and we should thus remove from them those Jelly-fishes which do not 

 pass through an alternate generation. The peculiar character of the 

 marginal ap23endages of the Trachyneinida?, so different from anything 

 found among the true Hydroids, and which resemble so closely those 

 of the Charybdeida?, is another character in favor of this division, as 

 weU as the nature of the veil, which is a thick, solid, folded membrane, 

 approaching somewhat in character the actinal pouches formed by the 

 veil of Camj)auella. 



Campanella pachyderma A. Agass. 



Tliis small Medusa is jiarticularly interesting on account of the light 

 it throws on the systematic position of the iEginida\ Having the gen- 

 eral appearance of the ^ginidae, it has, however, distinctly marked 

 radiating and circular tubes ; the genital organs are developed, as in 

 that fiimily, in horseshoe-shaped pouches arninged round the base of 

 the proboscis, which projects through a small space left by the pendent 

 folds of the veil beyond the level of its actinal surface. The circular 

 tube is thus apparently placed at nearly one third of the height of the 

 bell, owing to the great expansion of the eight lobes of the lower floor. 

 The veil is attached at the inner extremity near the genital pouches, 

 and between every two of the chymiferous tuJjes it is drawn up, form- 

 ing a distinctl}- marked indentation. The position of the genital pouches 

 is very similar to what we find among other Discophonis, as the Lucer- 

 naria^ and Cuninido", for instance, where they form an elongated lobed 

 rosette round the centre. The genital pouches extend in a continuous 

 line round the base of the proboscis. The .shape of the l)ell is a some- 

 what depre.ssed hemisphere, flaring slightly at the base ; the tentacles 

 are carried somewhat stiffly (Fig. 71)), and are capal)le of but limited 

 contraction and expansion ; the proboscis equals in length the height 

 of the bell ; it is conical, and terminates in a smooth opening. The 

 veil is not very opaque, and when the medusa is seen from the actinal 

 side (Figs. 71, 72), the chymiferous tubes, as well as the circulai* tube, 



* From tlie fi^xure given by Gt'p'nhaur of tlie ])e'dmKulated marginal bodies in Aglaura, the 

 affinity to Trachyuuma (Circe) is un(jiiestionable. 



