Note 1 — PREFACE.

I feel under special obligation to Mr. Dana for several very interesting communications connected with the present subject, and for information derived from his magnificent work on the Crustacea, collected during the United States Exploring Expedition. Also to M. Bosquet, of Maestricht, for the loan and gift of several interesting fossils, described and illustrated with the utmost fidelity, in his beautiful “Monographie des Crustacés fossiles du terrain Crétacé du D. de Limbourg.”