PREFACE. 11 



generic names and higher divisions of the group. Pomel gave a revision of the genera and 

 published a number of new ones. This part of his work was apparently based wholly on the 

 observations of others, to whom he gives neither credit nor reference. Waagen, and Miller 

 and Gurley published new species. Duncan revised the genera in his revision of the genera 

 of the class. Sollas, Gregory, Whidborne, DoUo and Buisseret, Girty, Bather, and Spencer 

 pubhshed new species or observations on older species. In numerous text-books, figures and 

 more or less full descriptions are of course given, wholly or mainly from the observations of 

 others. The important monographs of A. Agassiz, Loven, and Mortensen have been constantly 

 in hand for comparative studies of recent types. The late lamented Alexander Agassiz stands 

 unique in the history of echinology, for his work on the group extended over a period of nearly 

 fifty years, during which time he published numerous extensive monographs besides many 

 smaller papers. 



The attempt has been made to give full credit to the above authors for their observations. 

 While I have not always been able to agree with the observations or conclusions of others, it is 

 to be remembered that these fossils have a complex structure and are often very imperfectly 

 preserved, so that they are exceptionally difficult to study. Also, I have had the privilege of a 

 fuller opportunity than probably any one before to study a large range of Palaeozoic species. 

 Those who are most familiar with the group can best appreciate the difficulty of avoiding errors, 

 as I hope may be remembered in my own case. Barring possible oversights, the systematic 

 part of this paper includes every pubhshed species, practically all of which are figured. A 

 figure is given of all recognized species excepting Archaeocidaris rankini, A. prisca, and Konincko- 

 cidaris cotteaui of which no specimen was available and no figure has been published. Also 

 excepting Pholidocidaris gaudryi of which the published photographic figures are too indistinct 

 to be safely copied. The location in museums of types and rare species is given as an aid to 

 investigators. 



For their kindness and liberality in allowing me freest access to material in collections and 

 for every facility in the use of the same, as well as other kindnesses, I would return grateful 

 thanks to the following curators and private collectors. My friend, Dr. F. A. Bather, of the 

 British Museum, to whom I am under special obligations, most kindly helped me by corre- 

 spondence and the loan of rare specimens, as well as by access to the rich material in the British 

 Museum. He also had the great kindness to borrow, study, and send me drawings and notes 

 on the specimen of Lovenechinus lacazei described from the York Museum. During a visit 

 at the British Museum I enjoyed the privileges of the rich library facilities there available. 

 Dr. F. L. Kitchin and Mr. H. A. Allen, of the Geological Museum in Jermyn Street, London, 

 helped in a similar way, and most kindly had photographs taken of some of their important 

 specimens as here reproduced. Professor Henry Woods, of Cambridge, England, and Pro- 

 fessor John Joly, of Trinity College, Dublin, gave access to their choice material. Dr. R. F, 



