iy PREFACE. 



Some errors have been detected, and if many more should not 

 be discovered by others, we shall be agreeably disappointed. 

 We have, however, some confidence that they will not exceed 

 in magnitude those which we have endeavored to eliminate from 

 Conchological literature. All are liable to error : but it may 

 be reasonably expected, that, as YD Astronomy rude approxima- 

 tions have been repeatedly corrected with successive advances 

 towards absolute accuracy, so in Zoology the errors respecting 

 geographical distribution and the characters of species will be 

 gradually eliminated. A real advance towards accuracy, how- 

 ever small, will be an ample reward for a labor which has been 

 performed con amore. 



For other valuable assistance, especially in the preparation of 

 Indices, I have been indebted to THOMAS BLAND, Esq. 



Some of the sheets having been issued while the work was 

 in press, the dates at the bottom of the first page of each sheet 

 may be taken for the dates of the publication of the new 

 species. 



