INTRODUCTION. vii 



had been available, the advantages to be derived from a study of it would have 

 been doubtful, inasmuch as in the greater number of the fossil forms the 

 characters on which the classification of recent species is based are not preserved 

 with sufficient clearness to admit of comparison. 



The Plates which illustrate the present volume have been reproduced by the 

 Collotype process by Messrs. Morgan and Kidd from negatives taken by myself. 

 For various reasons it was often found impracticable to represent closely allied 

 species on the same Plate. As isochromatic plates were chiefly used, the 

 diff'erence in the depth of colour of the various specimens accounts for the 

 variation in intensity of the figures on some of the Plates. The scale on which 

 the specimens are figured is also not constant, and depends entirely on the 

 reduction necessary for each specimen or group of specimens in order to fill a 

 10- by 8-inch plate. I trust that sufficient detail will be found in the figures to 

 give a good idea of the habit of the specimens, and also, although necessarily to a 

 less extent, of the form, angle, and variation of the corallites. 



GEORGE BROOK. 



