17li INTRODUCTION 
Natural History of Cuba, we cannot forbear making use 
of some of the interesting information that it affords, 
and also of facts contained in the meinoir of Dr. Pfeiffer 
■ in the pneumohranchiate mollusks of the same island. 
In this connection also, the results of the observations of 
M. D'Orbigny in South America, in their relation to the 
distribution of the terrestrial species on this continent. 
gain an additional importance. We compare therefore 
the genera of Cuba, and of South America, with those 
of the United States. It is not to be supposed that 
these lists are ecpjally complete with that of the United 
States ; indeed it may be taken for granted that they 
are much less so. Being the work of foreign travellers, 
who resided but a short time in those countries, many 
species must have necessarily escaped notice, however 
careful their researches may have been ; and whenever 
the subject shall be resumed by native naturalists, the 
gleanings may be expected to equal in number the first 
harvest. But they probably represent pretty nearly the 
I in '] lortion in which the respective genera prevail, and 
may, therefore, serve our present purpose. 
It is proper to observe, before introducing the follow- 
ing table, that the researches of M. D'Orbigny were 
mostly confined to that part of South America which 
lies north of the twenty-fifth degree of south latitude, 
and that a large majority of his species appear to have 
been collected in Bolivia, Peru, and Colombia, on the 
western side of the continent. 
