A CJTHORS' PREFACE. 



The present work is the result of our joint study of the Blastoidea, which has been 

 ranied on for the past seven years, though with a considerable amount of interruption 

 owing to our official duties and to the pressure of other engagements. It originated 

 in a strong desire to investigate the structure and relationships of this interesting 

 group of extinct Echinoderms by the light of the recent advances in our knowledge 

 of their living representatives. 



The additions to our knowledge of Echinoderm structure which we owe to the 

 genius of Johannes M tiller no doubt largely influenced Professor Ferdinand Boemer 

 when preparing his classical work on the Blastoidea, which is now moi - e than thirty- 

 five years old, and must be regarded by all as a model of precise and accurate descrip- 

 tive Palaeontology. 



But recent discoveries have furnished so much additional information as to the 

 relationships of the Stalked Echinoderms, that they are now viewed in quite a different 

 light from that which was shed upon them by Miiller's memorable researches. Under 

 these circumstances, the interest attached to a renewed morphological investigation of 

 the Blastoidea attracted us very strongly. Our chief difficulty, the want of adequate 

 material, was soon and simply solved ; for Mr. Charles "Wachsmuth, of Burlington, 

 Iowa, whose admirable work on the Palaeocrinoids is known to every palaeontologist, 

 generously offered to place at our disposal a selected series from his fine collection of 

 American Blastoids, which should be specially adapted for the exhibition of structural 

 characters. 



The collection reached us in April, 1881 ; and though it was originally lent for six 

 months only, the owner's liberality has enabled it to remain in our hands for over 

 five years. Nothing that we can say can express better than this statement the extent 

 of our indebtedness to Mr. Wachsmuth's generosity, which prompted him to expose 

 a valuable collection to a double journey across the Atlantic and a prolonged 

 detention in this country, in the hope of promoting scientific knowledge. We 

 wish that we could regard the results of our work as at all commensurate with 

 our feeling of indebtedness to Mr. Wachsmuth, with whom we are sorry to find our- 

 selves at variance upon certain morphological questions. But it is perhaps scarcely 



