PREFACE BY THE EDITOR. 
Tue voluminous work which the Ray Socrery 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 ke 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 Socrery, 
whose Council were so convinced of its value, that they re- 
