ART. 13, DERMANYSSID MITES OF NORTH AMERICA—EWING. 3 
the number of families in the Acarina has been increased at an 
entirely too great a rate in recent years. 
The other new subfamily created, the Lntonyssinae, is established 
for the genus Entonyssus, with its single species, also new. This 
species was taken by Doctor M. C. Hall from the air sac of a snake. 
In Entonyssus each chelicera has one arm provided with a single 
hook (fig.1), but the hypostoma is without hooks. 
GENERIC CHARACTERS IN DERMANYSSIDAE. 
Recent workers have recognized but few genera in this family. 
The reasons for this are in part obvious. First, the genera proposed 
by the earlier workers, and more especially those proposed by 
Kolenati in 1859, were either based upon immature individuals or 
upon characters which could not be accepted as valid in the light of 
what is known about generic characters in related mite families. 
Second, but few of our recent mite specialists have had any consider- 
able number of species to work with. 
On account of this latter fact the present writer has been deterred 
for years in attempting any generic analysis of the group. Now, 
however, a sufficient amount of material is at hand to justify such 
an attempt. Tor the purposes of this analysis the genus concept 
will be defined as follows: A valid genus is a taxonomic category 
including either a unique species with one or more characters of a 
more fundamental nature than those used in specific diagnoses of the 
most nearly related species, or a category including a group of closely 
related species the majority of which possess at least two correlated 
characters of more than commonly recognized specific importance 
in the next larger group to which the genus belongs. The family 
Dermanyssidae does not lend itself so easily to generic anaylsis as 
the Gamasoidea as a whole does. 
KOLENATI’S GENERA. 
Kolenati (1859) was the first to make any extensive study of the 
group. In his Beitrige zur Kenntniss der Arachniden he not only 
proposes several new genera for the reception of his various species 
but divides the group into the following subgroups, for which 
English equivalent names are substituted: Fat mites, dirty mites, 
big mites, rough mites, broken-shield mites, and jointed-shield mites. 
Although written in a more or less popular manner, Kolenati’s work is 
of high scientific value, and the species he describes are so well illus- 
trated that no serious difficulty should be encountered in grasping 
their taxonomic value. The chief difficulty in passing on Kolenati’s 
work is that he did not differentiate between the sexes or between 
nymphs and adults in his descriptions. Also in many instances one 
can not tell whether a drawing was made of a male or female or a 
