360 GEOGRAPHICAL DISTRIBUTION. 



dispar, D. mitra, and Galenlaria australis illustrate the same point though in 

 less degree. 



Although the Sij)honoi)hores show the quantitative difference between 

 the two regions in a well-marked fashion, it is much more extreme among the 

 Medusae. Thus Rhopalonema and Aglaura were represented at the "barren" 

 stations by only one or two individuals, if at all, instead of by swarms, as in the 

 Current (Bigelow, :09a, p. 223). In other words the Siphonophores are much 

 more evenly distributed quantitatively than the holoplanktonic Medusae, 

 though less so qualitatively. 



Up to the time of the Expedition, the following well-authenticated species 

 of Siphonophores had been described from the Tropical Pacific, under various 

 names : — 



Sphaeronectes truncata Agalma okeni 



Cuboides vitreus Stephanomia amphitridis 



Pray a cymbiformis Stephanomia bijuga 



Nectrodoma dubia Physophora hydrostatica 



Abyla leuckartii Athorybia rosacea 



Abyla trigona Anthophysa rosea 

 Abylopsis tetragona 



Abylopsis eschscholtzii Rhizophysa filiformis 



Bassia bassensis Rhizophysa eysenhardtii 



Diphyes appendiculata Physalia utriculus. 



Diphyopsis chamissonis Porpema prunella 



Diphyopsis dispar Porpita pacifica 



Velella lata 

 Ersae bojani 



and likewise the genera Hippopodius, Galeolaria, Forskalia, Apolemia, Ste- 

 phalia, and Epibulia have been recorded, for species whieli can not now be 

 identified with certainty. 



Of the twenty-five identifiable species, no less than twenty-two are repre- 

 sented in the "Albatross" collection, and of the remaining three, one, Athorybia 

 rosacea, is a form which has seldom been taken anywhere. Most of the species 

 were previously known from the Pacific by a few scattered captures only. Indeed, 

 the only ones which have been recorded often enough to allow their distribution 

 to be plotted for the Pacific as a whole are Velella and Porpita. Both of these 

 genera are very generally distributed over the entire tropical and subtroi)ical 

 regions of that ocean, and most of their recoi-ds lie within the isotherms of 

 ()8°F., for the hottest months of the year. There are a few records of Velella 



