Chap. VI. GEOGRAPHICAL DISTRIBUTION. 177 



SECTION II. 



GEOGRAPHICAL DISTRIBUTION OF THE DISCOPHOU^. 



Although there are extensive tracts of the sea, the Discophorse of which have 

 never been noticed, and there are also vast regions, probably including several 

 distinct Faunae, the Acalephs of which are entirely unknown, it is, nevertheless, 

 already possible to draw interesting results from the data on hand, especially by 

 comparing the character of the Faunae which have been extensively explored, with 

 the few types known from other quarters. The accessions furnished by the United 

 States Exploring Expedition, under command of Captain Charles Wilkes, the data 

 obtained from Mr. W. W. Wood, and the observations of ray son along the coast 

 of Oregon and California, are highly valuable in that respect, as affording the means 

 of contrasting the Faunae of the Pacific coast of North America, of Terra del 

 Fuego, and of China, with those explored by Eschscholtz, Mertens, Lesson, and the 

 resident naturalists of Eui-ope and North America. 



It appears from the data recorded in the preceding tabular view, that the 

 lowest Discophorae, the Lucernariadse, are the only ones which extend to the boreal 

 Fauna?, and that some genera, Aurelia and Pelagia for instance, are cosmopolites, 

 while others, such as Cyanea proper, are peculiar to the northern hemisphere ; others 

 are tropical, such as Mastigias, Leptobrachia, Cephea, Polyrhiza, Diplopilus, and Hy- 

 droticus; others still, Rhacopilus, Placois, and Lobocrocis, are only to be found in 

 the southern hemisphere, and many are quite local in their distribution, as, for 

 instance, the genera Stomolophus, Stylonectes, Cotylorhiza, Sthenonia, Phacellophora, 

 Heccfedecomma, Couthouyia, Medora, Desmonema, and Marsupialis proper. The 

 grouping of the species in their respective zoological provinces is also interesting 

 to notice, and shows that every region of the ocean has its own species, variously 

 associated. It is much to be regretted that the localities from which many of 

 the species described by older writers were obtained, are not given with greater 

 precision, as they cannot now be referred with accuracy to their Faunae. 



It is not yet possible to separate, with precision, the arctic and boreal Faun*, 

 as far as the Discophorae are concerned. In the Celtic Fauna we find Rhizostoma 

 Cuvierii, Holigocladodes lunulatus, Aurelia cruciata, Cyanea capillata and Lamarckii, 

 Chrysaora hysoscella, Polyxenia Alderi, Lucernaria quadricornis, which is rather boreal, 

 inauriculata, campanulata and auricula, Depastrum stellifrons, and Carduella cyathi- 

 formis, the latter boreal only. In the Acadian Fauna, we find Aurelia flavidula, Cya- 

 nea arctica, Lucernaria quadricornis, if identical with the European, and L. Fabricii ; 



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