PREFACE 



The last quarter of a century has been an important 

 period for the science of Cx)nchology. While many 

 private collectors have been gathering specimens of all 

 kinds, and incidentally making many new discoveries, the 

 universities have been establishing seaside laboratories, 

 the Government sending out exploring vessels, and the 

 learned societies putting forth many publications. Es- 

 pecially has the National Museum at Washington been 

 issuing its valuable bulletins, embodying the conclusions 

 of its painstaking investigators, and making available the 

 results of much labor. 



This activity has resulted in the accumulation of much 

 new material, and incidentally the changing of many old 

 names. The latter work is an ungracious piece of busi- 

 ness at best, and has seldom been indulged in wantonly. 

 But new views on the subject of classification, new 

 researches into former systems of nomenclature, and 

 an enlarged knowledge of the fossil progenitors of exist- 

 ing species, have compelled the readjustment of what 

 before seemed settled. 



It is comparatively easy, when collecting in a small 

 field, to separate the specimens into fixed and definite 

 groups ; but as one's observations become extended, the 

 varieties multiply, and increased knowledge of both facts 

 and records causes embarrassment. The necessary 

 changes, however, even of familiar names, must not be 

 too deeply regretted, for they indicate a real advance in 

 our conception of the great plan of Nature. 



