vi PREFACE. 



Mr. Power, and to all who have with friendly mind and ready hand helped me, I now return my 

 hearty thanks. 



It ought to be mentioned that the Royal Society has granted a Hundred Pounds towards 

 the expenses of the Plates for this Memoir ; and also that, in putting my drawings on stone, 

 in drawing some of the objects from nature, and in colouring the figures, Mr. George West has 

 shown his usual facility and conscientious care. 



