PREFACE. 



The materials of this Monograph have been accumulating for more than ten years ; 

 but the obscurity of some of the specimens, and the necessity of obtaining direct infor- 

 mation from friends, both at home and abroad, acquainted with these fossils and the strata 

 in which they are found, have caused considerable delay. Other interruptions, especially 

 of late, have also thrown me off the study. Still the protracted time has brought many 

 new facts to light regarding Estherice, both recent and fossil, as well as several new 

 species and varieties. 



I have been careful to give a full account of localities, and of sections in par- 

 ticular, that enquirers may seek for more specimens, and that they may be still more 

 careful than heretofore in noting the exact contents and characters of the Estherian and 

 associated strata. As fossil Estherice occur mostly in the passage-beds between the 

 great Formations, and in the estuarine and freshwater equivalents of the marine portions 

 of those Formations, the exact study of the Estherian beds cannot but prove of value in 

 Geology, though the correlation of the beds may be somewhat difficult. The early 

 appearance and long continuance of the Estherian type, and its wide distribution, are 

 subjects of great interest to the Palaeontologist. 



I have a host of friends and kind helpers to thank for the assistance which they have 

 rendered me, in various ways, always readily, and often at a considerable cost of time and 



