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the present were a fit occasion for such minute inquiries, the investigations of the various known species of Microscopic shells would unfold a æries of contrivances having relation to the economy of the minute Cephalopods by which they were constructed, not less striking than those we have been examining in the shells of extinct Genera and species of larger Cephalopods. M. D'Orbigny has noticed from 600 to 700 species of these shells, and has prepared magnified models of 100 species, comprehending all the Genera.

The greater number of these shells are microscopic, and swarm in the Mediterranean and Adriatic. Their fossil species abound chiefly in the Tertiary formations, and have hitherto been noticed principally in Italy. (See Soldani, as