TO 



THOMAS BELL, F.R.S. &c. &c. 



This Work, a development of a paper submitted, in fulfilment of his wish, to the 

 Linnean Society, which prospered under his Presidency^ and in which he continues to 

 take the warmest interest, is affectionately inscribed by his old friend and fellow-labourer, 



THE AITTHOB. 



