ARACHNIDES. 
507 
ORDER II.—TRACHEARLE. 
Instead of a heart provided with a single dorsal vessel, they 
perspire by radiated tracheae, and receive the air by spiracles 
placed in the abdomen or thorax; sexual organs single ; eyes 
usually two, but never exceeding four, and some species are de¬ 
void of them ; most species have a syphon-shaped mouth. 
TRIBE I.-PYCNOGONIDES. 
With a projecting tubular syphon; four eyes placed on one 
tubercle ; feet frequently very long, and provided with unequal 
hooks ; two oviferous feet at the base of the first.—The genera 
are, 1. Nymphon ; 2. Ammothea; 3. Phoxichilus; 4. Pycno- 
gonon. 
Genus 3. — P H O XIC HIL U S. —Latreille. 
Generic Character. — With extremely slender legs; the mid¬ 
dle joint of the thigh longest, and subclavate; first joint of the 
tarsi very small; claws double, unequal, the longer one sharp; 
the ova-bearing legs, with seven joints, the last one somewhat 
tuberculous, and inserted at the base of the rostrum, one on 
each side, and attached to the first segment of the body. 
Phoxichilus hirsutus. — The Hairy Phoxichilus. 
Plate XCVI. fig. 9. 
The articulations of all the joints of the limbs provided with 
hairs. 
TRIBE II.-PSEUDOSCORPIONES. 
With very large pediform palpi, either terminating in didac- 
tyle forceps, or in a vascular button without any hook.—The 
genera are, 5. Obisium; 6. Chelifer; and 7. Galeodes. 
Genus 5. — OBISIUM.— Illiger. 
Generic Character. — With a cylindrical body, and the thorax 
consisting of one segment; mandibles porrect; and four eyes. 
Obisium Trombidoides. — The Trombidoidal Obisium. 
Plate XCVI. fig. 10. 
The second joint of the arms considerably elongated •, fingers 
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