of several New Shells. 29 
have not been backward in expressing their warm attachment to 
the plan of the great Swedish naturalist. It is not my present inten- 
tion to speculate upon the respective merits of these systems. In the 
study of no class of the animal kingdom have there been so few ab- 
solute facts discovered, whereon to build a truly natural system, as 
in that of the testaceous mollusca, In the history of those families 
which: are known, anomalies have been discovered, which bafile 
explanation, and obstacles almost insurmountable, from the very 
nature and hab:tat of the animals, conspire to retard that rigid in- 
vestigation of their economy, which must alone form the basis of 
their perfect arrangement. 
But while so many writers have been engaged in forming systems 
and constructing genera, the elucidation of species has compara- 
tively been neglected. 
An extensive acquaintance with species is the first step to a 
knowledge of natural divisions. In every branch of natural history 
those who have seen and studied the fewest individuals, will be 
most apt to create new genera; ‘‘ when they have seen more, they 
will discover the intermediate links which unite different genera; 
and thus be forced to join what they formerlyseparated*”. Iam 
fearful this has not sufficiently been considered by the authors and 
advocates of the French systems: it may be doubtful if their generic 
distinctions are not too much refined ; butit is certain that a know- 
ledge of the science is daily becoming more unattainable to all but 
professed naturalists. 
While this revolution of classification and of genera is going on, 
our cabinets are crowded by innumerable species, some of which 
we know not how to name, while others (well known by the figures 
of the older writers) remain undescribed: new species are con- 
tinually pouring in upon us to augment the number: and although 
the student may be perfect in the elements of his system, he knows 
not how to proceed, or where to turn, if he ventures on the inyesti- 
gation of species, 
The volumes of Lamarck (His. Nat. des Animaux sans Ver- 
tebres) have indeed done much to remedy this evil. They contain - 
* Wildenow, Principles of Botany, P, 175, “Sect, 163, 
