PREFACE. 
Tuis short preface is intended both as an explanatory notice and as a 
dedication. Without the aid of my friend Mr. M‘Annrew, the following 
Monograph could not have been drawn up. The mass of the materials 
employed in its construction was the produce of several delightful scientific 
cruises, when I accompanied him in his Yacht, the Osprey. Nine 
years ago this history was commenced: were it not for the ardent friend 
of science, whose name I wish to associate with my work, as many more 
would be required for its completion. Even now, I can offer only an 
outline of a most curious and interesting, though neglected, department of 
British Zoology. The greater part of the matter in this essay is new. With 
one exception—kindly communicated by Mr. Alder—every species has been 
examined by myself. Every figure is original. Any defects in the 
engravings must be laid to my charge; their merits are due to my friends 
Mr. W. Baily, and Mr. C. R. Bone, for whose exertions [ have to return 
many thanks. 
Epwarp Forses. 
London ; June 25, 1848. 
