426 A HISTORY OF RECENT CRUSTACEA 
perzeon; the face is sloping. The sides of the head are 
distinctly marked by a vertical marginal line and an infra- 
marginal line. The clypeus is arched.’ The pleon has six 
segments, of which the first two are narrower and usually 
shorter than the third. The young quit the mother with 
the seventh segment of the perzon still undeveloped. 
The first antennze are three-jointed. The second antennz 
have the flagellum from two- to four-jointed. The first 
maxille have two plumose setee on the inner plate; the 
second maxille have two plates; the ‘ palp’ of the maxilli- 
peds is two-jointed, the epipod oblong, acute. The trunk- 
feet are rather long. In the first and second pleopods of 
the male the inner branches form long narrow sexual 
organs, those of the first pair often coalesced; in the 
female the same branches are rudimentary, short, acute. 
In the remaining pairs the inner branch is branchial; in 
all the pairs the outer branch is opercular, and often also 
tracheal. The uropods are always prolonged beyond the 
two terminal segments of the pleon. 
Budde-Lund, in his exceedingly valuable work on the 
Terrestrial Isopoda, makes a family Onisci, which he divides 
into two sections, Armadilloidea and Oniscoidea, but it 
seems better to constitute two families, since it is the 
almost invariable fate of large sections eventually to be 
made independent. For the Oniscide, or second section, 
Budde-Lund gives a tantalising ‘Conspectus Generum,’ 
based on the flagellum of the second antennz, on the 
tracheal or non-tracheal character of the pleopods, and on 
the uropods. 
I. Flagellum 2-jointed. 
A. With tracheez. 1. Porcellio. 
B. Without trachez. 2. Platyarthrus. 
II. Flagellum 3-jointed. 
A. With trachez. 3. Scleropactes. 
B. Without trachez. 4. Oniscus. 
IIL. Flagellum 4-jointed. 
A. Uropods short. 5. Armadillonisecus. 
Lb. Uropods elongate. 6. Deto. 
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