206 GEOGRAPHICAL DISTRIBUTION. 



fauna, — the Lusitanian, the West African, the Tropical Atlantic, and the 

 American Boreal forming the base of life as it were of the Atlantic Realm. 

 It is not a little remarkable that the point urged by Sars with so much 

 force (in absence of evidence) against Loven's theory of the distribution 

 of life, — of a uniform fauna throughout the bottom of the deeper parts of 

 the Atlantic, — should so soon have been disproved by actual exploration; 

 the presence of Rhizocrinus lofotensis, Schizaster fragilis, Homolampas fra- 

 gilis, Echinus norvegieus, Dorocidaris papillata. Echinoeyamus pusillus, at 

 such widely distant points and with such great bathymetrical range, shows 

 that the theory proposed by Loven gives, as far as we know, a rational ex- 

 planation of many phenomena hitherto imperfectly understood in the distri- 

 bution of marine life in the different bathymetrical hells. The explorations 

 now going on under the auspices of the United States Coast Survey will 

 probably extend our knowledge on this subject so materially that it 

 seems useless to attempt any further exposition of the subject till their 

 results are available, and 1 will limit myself, in discussing the geograph- 

 ical distribution of Echini, to strictly littoral divisions; not that I do not 

 expect the material likely to he collected will not modify to some extent 

 the limits assigned to the littoral divisions here sketched out. hut in the 

 main they are likely to be tolerably correct, if we ma\ judge from the na- 

 ture of the material thus far brought together in different public museums 

 of Europe and America by the exploring expeditions sent at different times 

 during this century by all the great continental nations. They have ex- 

 plored more or less thoroughly the shore lines at least of the greater 

 part of the world, leaving but few spots about which we actually know 

 nothing, so far at lea-1 as the distribution of Echini is concerned. It was. in- 

 deed, a matter of great surprise to find how few species of Echini hitherto 

 not noticed were not to be found in the vast stores of the British .Museum, the 

 Jardin des Plantes, the .Museums of Copenhagen. Stockholm. Berlin. Vienna. 

 Everywhere, although from different localities, were found repetitions of spe- 

 cies already well known, so that in making a map of the littoral regions we 

 find but short stretches of shores completely unexplored. Of course addi- 

 tional species will undoubtedly turn up even in the best explored localities, 

 but we have probably a very fair representation of the littoral Echini of the 

 world. 



In following out the geographical distribution of such a limited order as 

 the Echini, we have the great advantage of being able to carry in our mind 



