ON TRACHEAN ARACHNIDA. 
519 
Illiger, in a table, merely nomenclatory of the genera of 
the class insect a, which he has placed at the end of his work 
on the Coleoptera of Prussia, separates from the scorpions the 
species which Fabricius names cancroides , and cimicoides , to 
form a particular genus, which he calls obis turn y and which 
corresponds exactly with the chelifer of M, Latreille in his 
Summary of the generic characters of insects, published 
anteriorly to the work of M. Illiger* Dr. Leach, adding 
some new observations to the preceding, has preserved the 
genus obisium of Illiger, but restrains it to the genera of 
cheliferi, which have four simple eyes, the body almost cylin- 
drical, and the eight posterior feet composed of six articula- 
tions. The species in which the feet have but five articula- 
tions, whose body is depressed, and presents but two simple 
eyes alone, form the genus chelifer, of this gentleman. ( Zool . 
MiscelL vol. iii. p. 48.) He places these two genera in the 
family of the scorpionidea. 
Although it cannot be denied that these arachnida have, in 
their general structure, a great resemblance to the scorpions, 
they appear, nevertheless, to differ from them in some anato- 
mical considerations. They present but two stigmata, situated, 
one on each side, above the origin of the two anterior feet. 
M. Latreille has, therefore, placed this genus, in his family of 
Pseudo -scorpiones , which immediately succeed that of the 
scorpionides . If it be true, that M. Fischer has observed in 
these animals, and the galeodes, respiratory organs, similar to 
those of the araneides, the family of false scorpions, composed 
of these two genera, should naturally terminate the order of 
pulmonary arachnida. 
The cheliferi have the body ovoid and depressed, or oblong, 
and almost cylindrical, invested with a dermis somewhat 
coriaceous, almost smooth, or but slightly furnished with 
hairs. It is composed, 1st. of an anterior segment much the 
