viii PREFACE. 



both parties, if those who desire an exchange would remember 

 that the smaller and smallest species possess the greatest interest 

 for me, and if they would at the same time point out to me such 

 families as they are chiefly desirous of knowing. Moreover, it will 

 be necessary to agree about the way in which the equivalents might 

 be forwarded. In case I receive no such direction, I shall suppose 

 I am at liberty to send them by the kind intervention of the 

 Smithsonian Institution at "Washington, through which I beg all 

 consignments intended for me may be forwarded. 



I have no doubt as to a successful issue to my labors, if I con- 

 tinue to receive the same liberal and generous assistance from the 

 Smithsonian Institution and from Baron Osten-Sacken which I 

 have enjoyed from the beginning, especially if this commencement 

 contributes to increase the number of those interested in the study, 

 and ready to promote it by the communication of species taken by 

 them, in the same way in which Messrs. Rob. Kennicott, S. H. 

 Scudder, A. S. Packard, Edw. Norton, and others, have furnished 

 materials for the excellent paper of Baron Osten-Sacken on the 

 Limnolidx of North America. 



H. LOEW. 



Meseritz, 3 Oct. 1S60. 



