viii. PREFACE. 



obvious to the practiced eye, of the cxi'vikucccI col- 

 lector. 



Among these is the jxirticular thing whi- . 1 wish 

 to direct attention to here, viz.: the dl-irr uv.-iru nt 

 of the RiKTcics, in the genera. It will u: o;j^cr\cii, 

 ihal while the genera have l)een arranged in their 

 l»roper natural order, the s|Kcies are often ;n^>ui>ecl, 

 in the text, quite olhen»'isc. The reason 1 have 



taken those sjKrcies, in genera which contaui Mrveral, 

 for treatment first, which, on account of their common- 

 iHss, or |K!culi.ir habitat or at.»M innr.- rnii!d Ik; most 

 exsily and ccruinly identificti. i ruin lacic, 1 have, 

 j.r.M ceded step by step, to the more difTicuh pbnts. 



'l"hen again, I have often found it convenient, to 

 group certain species tc> ior the advantage of 



« .MniKirison, in the descnpuuu, which do n' 

 naturally iK^long together. Vou will therefore under- 

 stand, that while the ««r.^r^ nn.! rcnera, folium- their 

 natural grouping, in uic ic\i, uic specici in the 

 genera cannot l>e depended upon to do so, in most 



1 ases. 



I must add a single rcmnrk firthcr, on this ircncrnl 



subject. While the sc\'craj iuu-Liasscs, tiie Oreen, 



