DISTRIBUTION OF BRITISH ECHINODERMS. 181 



It is obvious that, if there be a natural British area, that area 

 must be limited in depth as well as in extent, and the bathymetrical 

 limit must lie at the point where the coast of Britain becomes con- 

 terminous with the continent of Europe. Outside this the land 

 sheers rapidly downwards, and not far from the mouth of the 

 English Channel the dredge will sink for more than 2000 fms. 



But, for Echinoderms at any rate, there is no natural British 

 area : Shetland belongs as certainly to the Scandinavian area as do 

 the Channel Islands to the Lusitanian, or the deep water off Ireland 

 to t lie general Atlantic fauna. 



The only conclusions, therefore, which we need attempt to reach 

 are such as may be of interest to a collector who finds himself more 

 or less within hail of the United Kingdom. 



He will find that, if his apparatus be sufficient, he may dredge to 

 any depth with almost a certainty of finding Echinodeims. He 

 will often find them in profusion and sometimes in great variety. 

 He will find that the teaching of the earlier marine zoologists as to 

 zones or belts of animal life is hardly confirmed by the extension of 

 such characteristically shore forms as the Common Sea-Star or the 

 Heart-Urchin to, respectively, 120 fms. and 85 fms. Forms which 

 he has dredged from a few fathoms, like the Fiddle-Urchin, will be 

 found at a depth of more than a hundred times ten fathoms, or, 

 like Ophiacaniha bidentata, to extend from 20 to 2000 fms. 



Of a number of Echinoderms found within a few hours' or days' 

 sail of the British coast, we know far too little ; nearly every deep- 

 sea dredging increases the bathymetrical range of familiar forms, 

 and there is, doubtless, much work to be done in the future. 



Well known forms, if taken from considerable depths will often 

 appear at first sight to present important points of variation from 

 specimens already known, but comparison with a large series will 

 often show that they are only some of the many varieties of a 

 widely-distributed species. 



Table Y. — Distribution of Echinoderms within the British Area. 



The distribution of the British Echinoderma within the artificial 

 region selected offers some points of interest : for example, the area 

 of the Xorth Sea contains far fewer species than the western coasts 

 of our islands ; a number of the forms here catalogued are confined to, 

 or, to speak more strictly, are only known as yet from, the Faeroe 

 Channel, and the fauna of the Channel Islands is very different from 

 that of Shetland. 



I proceed, therefore, to give a Table of Distribution for nine 

 areas, which will, I think, be found generally useful to the collector. 



