PART III. 



PALAEOZOIC ECHINI. 



In considering the systematic part of this memoir, attention is called to the general state- 

 ments of the history of the subject, sources of material, methods of work, etc., as given in the 

 Preface and Introduction. The morphological part of this memoir is based in considerable 

 part on the study of Palaeozoic species, so that considerations of these older forms and their 

 relations are scattered all through the morphological sections. As references to the pages of 

 these earlier considerations of Palaeozoic genera and species can be gathered from the index 

 they are largely omitted in the descriptions. 



A key to the classification of Palaeozoic Echini is given in the last section (p. 201-208), 

 and a systematic table (p. 209), showing the genealogical relations, as understood, of the Palaeo- 

 zoic Echini to each other and to the larger groups of the post-Palaeozoic Echini. An asterisk 

 before the name of a species indicates that specimens have been studied. Under each species 

 the synonymy is given in full as far as ascertained, and references to the principal literature. 

 Miss Klem (1904) has recently published so full a list of references in her Revision of Palaeozoic 

 species, that it seems unnecessary to repeat minor references. All text-books are omitted 

 unless there is special need of comment, also works in which species are simply listed without 

 description or discussion, as Miller's Catalogue of North American Geology and Palaeontology, 

 Etheridge's and Morris's Catalogues of British Fossils, d'Orbigny's Prodrome, Dujardin and 

 Hupe's Echinodermes, etc. Where species are simply listed without description or discussion, 

 as in parts of Loven's (1874) and Miss Klem's (1904J memoirs, no reference is deemed necessary. 

 Messrs. Lambert and Thiery's Essai de Nomenclature (1910) has recently come to hand (March, 

 1911). Their distribution of Palaeozoic species in genera and their generic synonyms do not 

 appear to me well considered. Wliile there are no descriptions of species in Lambert and 

 Thiery's Essai, names from this work are included as a matter of synonymy. In my descrip- 

 tions of species I have given what are considered the essential features with new matter. 

 Where further information is desired, it may be obtained from the authors cited. 



Geological Distribution. 



Considering in brief and in a broadly inclusive way the geological distribution of Palaeozoic 

 Echini, their occurrence in formations is as follows. In the Ordovician, Echini are known only 

 from Russia where the primitive genus Bothriocidaris is represented by three species. 



(235) 



