MYRIAPODA. 
509 
TRIBE V.-HYDRACIINELLiE. 
Feet adapted for swimming. — The genera are, 19. Hydrachna-, 
and 20. Limnochares. 
Genus 19.—HYDRA C HN A.—AT«//er. 
Generic Character .—With subcylindrical porrect, inflexed four- 
jointed palpi, the last joint acute ; mouth protruded into a coni¬ 
cal rostrum ; body globose ; legs fringed with hairs, and at 
equal distances. 
Hydrachna geographica — The Geographical Hydrachna. 
Plate XCVII. fig. 2. 
Body globular, black, with scarlet spots and dots. Inhabits 
slow-running streams of Europe. 
TRIBE VI..-RICINI^E. 
Feet not constructed for swimming; animals somewhat am¬ 
phibious, wandering or parasitical—The genera are, 21. Bdelia ; 
22. Smaridia; 23. Ixodes; and 24. Argas. 
TRIBE VII.-MICROPHTHIRA. 
Having always six feet, and parasitical. — The genera are, 
25. Caris ; 26. Leptus ; and 27. Astoma. 
CLASS VIII.—MYRIAPODA. 
Head distinct, and provided with two antennae ; body divided 
into segments ; mandibles simple, incisive, most of which are 
provided with feet. 
The general structure of this class allies them with the Crus¬ 
tacea and Arachnides, but their respiratory organs connect them 
more closely with insects. The air is received into their bodies 
by numerous lateral spiracles ; they have, extending the whole 
length of their bodies, two tracheae, the one parallel to the other. 
They have single sexual organs; and an indefinite number of 
feet; and never fewer than six ; these are either arranged in 
double or single pairs, on each segment of the body, and in- 
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