PREFACE BY THE EDITOR. 



THE voluminous work which the RAY SOCIETY has here 

 undertaken to publish, has been mainly compiled by Pro- 

 fessor Agassiz, during the leisure moments of a life of almost 

 incessant scientific research. Originally prepared for his own 

 private use as an index to the numerous works on Zoology 

 and Geology which he had occasion to consult, the collection 

 gradually increased upon his hands, and the importance of its 

 publication as an aid to other scientific investigators became 

 daily more evident. Not trusting however to the means 

 within his own reach, he established an extensive correspond- 

 ence with naturalists in all parts of Europe, from whom he 

 received an immense addition of materials on the scientific 

 bibliography of their respective countries, and he was thus 

 enabled to prepare a catalogue, not indeed a complete one, 

 for that can never be attained in practice, but far more per- 

 fect than any existing, of all known works and detached 

 memoirs on Zoology and Geology. 



The utility of such a work to the scientific student is suffi- 

 ciently evident, yet its technical nature rendered its publica- 

 tion a matter of very doubtful policy to one who could ill 

 afford to sustain a probable loss. The work might therefore 

 have been indefinitely delayed, or never have seen the light 

 at all, were it not for the intervention of the RAY SOCIETY, 

 whose Council were so convinced of its value, that they re- 



