GENERA AND GROUPS OP THE ECHrNOIDBA. ^ 



urgently required. Hence in tliis *' Revision of the Genera and 

 great Groups of tiie Fossil and ileceiit Echinoidea," the Author 

 has endeavoured to remedy an urgent want. He has had unusual 

 advantages and opportunities for studying fossil and receut 

 Echiaoidea ; and in this endeavour to utilize them he is uader 

 great obligations to his friend A. Agassiz aud to the able natu- 

 ralists and palseontologists connected with the British Museum, 

 the Museum of Practical Geology, the Woodv^-ardian Museum 

 at Cambridge, to his colleague in the description of the Sindian 

 Eauua, Mr. Percy Sladen, and last, but by no means least, to his 

 kind and £:enerous friend Sven Loven. 



Note. — It will be noticed that many genera no longer find a place in 

 the classification, but are either removed entirely or placed as subgenera, 

 and, as the intention was to limit the genera rigidly, very few new ones 

 are introduced. In describing every genus, the name which comes imme" 

 diately after the generic term is that of the founder, and when it is in romaa 

 type it may be as sumed that the original definition was improved by the 

 naturalist whose name stands next. The names placed after the first one, 

 even when this is not in roman type, are those of subsequent investigators 

 and deseribers of species who have added to the value or have modified 

 the original diagnosis of the genus. When any anatomical details have 

 been described relating to a genus, the name of the investigator has been 

 added. The references, as a general rule, refer to the date, volume, and 

 page of works in which there are illustrations; but, to save space, the 

 number of the plate is not given, especially as it will be found upon the 

 page referred to. The distribution of the genera has, of necessity, been 

 considered, but the great geological formations alone are noticed in dealing 

 with the fossil forms. A description of the terms employed in the classi- 

 fication will be found at the end of the Essay. 



The synonymy adopted by A. Agassiz in his ' Revision of the Echini,' 

 1872-1874, is accepted. 



The classification of Dujardin et Hupe, in ' Les Suites a Buff'on,' was 

 a useful but not critical literary work, being a compilation. M. Pomel's 

 "Theses," Algiers, 1883, contain a classification which is not followed in 

 this communication, for the fundamental methods employed do not com- 

 mend themselves, it being impossible to admit genera which are not differ- 

 entiated by characters which have a decided and important physiological 

 value. 



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