10 PROCEEDINdS OF THE NATIONAL MIJSEVM. vol. xxvm, 



iind foriii.s that do not fit into ta])les. Several of the families are not 

 natural, and future study will greath' modify existing- systems. 



I have not made nianv new genera in the American mites. 1 l)elieve 

 in keeping genera as broad as possible. Division of a genus should 

 be made oidy on grounds of convenience or those of zoological neces- 

 iiity. Because a group of species in a genus diflers from the other 

 forms by some structural character, there is not, 1 think, sufficient 

 reason for a new genus. But whenever a species or group of species 

 difiers from the others by several disassociated points of structui'e, 

 together with differences in life history or habits, then a new genus is 

 advisable. However, in using an adopted classification it is sometimes 

 not easy to place a new form without either making, a new genus or 

 modifying the characters of existing genera. The history of Acarol- 

 ogv warrants the student in using nnicli caution in the creation of new 

 genera or higher groups. 



In regard to noiuenclature, I haAC not departed, save in a few cases, 

 from that in common acceptance among acarologists. In some fami- 

 lies there has been much difference of opinion, and lately Doctor 

 Oudemans, an able Dutch acarologist, has revised the nomenclature. 

 It is difficult to escape some of these changes, but others I can not 

 accept, nor go l)ack of 1T.5.S for generic names. The larger groups I 

 have called superfamilies, in accordance with the custom of the best 

 zoologists, and these divisions are practically the same as I used 

 in 1895. 



To the ordinary person mites do not exist. Occasionally he may have 

 painful evidence of their presence, but he has no idea of the numljer 

 of specimens and species around him. Yet a little careful searching 

 will reveal a world of these tiny creatures. Although Miiller early 

 described many water-mites and Hermann (1S04) and von Heyden 

 (1816) had gathered a few, yet this world of mites was practically 

 unknown until discovered by C. L. Koch a])Out 1840. Since then a 

 num))er of naturalists have partially explored its shores, and some- 

 times penetrated into the interior. Now there are about a dozen 

 persons who seriously study acarology and nearly as many more who 

 devote themselves to the water-mites. 



.SYNOPSIS OF SFPERFAMU.IES. 



1. Alxlomeii annulate, prolonged behind; very minute forms; often with lint four 



legs DEMODICOIDEA 



Ahdomen not annnlate nor prolonged behind; always with eight legs 2 



2. With a distinct spiracle upon a stigmal plate on each Hide of body (usually below) 



al)o\e the tliird or fourth coxie or a little behind; palpi free; gkin often coria- 

 ceous or leathery ; tarsi often with a sucker 3 



Xo such distinct spiracle in a stigmal plate on this part of body 4 



3. Hypostome large, furnished below with many recurved teeth; venter with fur- 



rows; skin leathery; large forms, usually parasitic IXODOIDEA 



Hypostone small, without teeth; venter without furrows; body often with coria- 

 ceous sliields, posterior margin never crenulate; no eyes GAMASOIDEA 



