204 



that do not pass to the European shores. Thus, there are two 

 faunae, quite distinct in some species, but having others also in 

 common, that pass from one to the other, through the Arctic seas. 

 Crossing now the American continent, we find, near lat. 50°, the 

 familiar forms of an Opkiopholis, very like Ophiopholis aculeata^ 

 and an AmpJiiura closely resembling A. tenuis ; there is still fur- 

 ther an Opkioglypha which at once recalls 0. Sarsii ; yet all 

 these are distinct species, illustrating faunae of a similar character. 

 Returning now to the east coast, and passing south of Cape Cod, 

 lat. 42^, we come on new species and leave the others behind. 

 Here is seen the genus Ophiura, (0. oUvacea,) an adventurous 

 traveller from more southern waters. At Charleston, near lat. 32°, 

 a set of species quite novel again surprises the naturalist ; here are 

 Ophiothrix angulata, Amphiura cordifera, and the slender-armed 

 Amphiura gracillima. This group has some analogy to that 

 found in the southern Mediterranean, but the resemblances are 

 faint, and no longer strike us like those of the northern faunce. 

 Still going southward, the fauna again changes, and near Cape 

 Florida, lat. 26°, the animal world of the Gulf of Mexico and the 

 Antilles opens upon us, with all its richness. Here are the char- 

 acteristic Ophiocoma crassispina, Ophiura appressa, Ophiopsila 

 Rusei^ Ophiothrix Orstedii, and many others. In Central Amer- 

 ica, crossing the few miles of land that separate the two great 

 oceans, we are surprised to find an Ophiuran fauna, the counter- 

 part of that of the Gulf; a fauna that is wonderful for its close 

 similarity and for its invariable difference. An unpractised eye 

 might well confound Ophionereis reticulata with 0. a7inidata, 

 Ophioco?na crassispina with 0. Ethiops, and Ophiothrix violacea 

 with 0. spiculata. Of the coast of California not enough is 

 known to make any comparisons. 



In reference to this paper, Prof. Agassiz made some 

 remarks on the principle which he thought ought to 

 govern zoological nomenclature ; viz : that each species 

 should be indicated, not necessarily by the name of the 

 first describer of the species nor by that of the one who 

 established the true genus, but by his who combines 

 originally or afterward the true generic and specific 



