ORDER ISOrODA. 
Arcturus, Latr., 
Are very remarkable for the form of the second and third feet, 
which are directed forward, and terminate by a long barbed 
articulation, and imperfect, or but slightly unguiculated. 
The anterior two are applied on the mouth, and unguicu- 
lated. The last six are strong, ambulatory, thrown back- 
wards, and bidenticulated at their extremity. In the relation 
of the length of their antennae, and the form of the body, they 
approach Stcnosoma. ( Arcturus tuber culatus, Lat.) 
The fifth section ( Asellota, Lat.) presents us with isopods 
with four very apparent antennae, disposed on two lines, seta- 
ceous, terminated by a pluri- articulate stem ; two mandibles, 
four jaws, usually covered by a sort of lip, formed by the first 
jaw-feet; vesicular gills disposed in pairs, covered by two 
longitudinal and biarticulate leaflets, but free ; a tail formed 
of a single segment, without lateral fins, but with two bifid 
stylets, or two very short appendages, in the form of tuber- 
cles, at the middle of its posterior edge. Some other appen- 
dages, in the form of lamime, situated at its inferior base, 
more numerous in the males, distinguish the sexes. 
Asellus, Geoff., 
Have two bifid stylets at the posterior extremity of the body, 
the eyes apart, the upper autenme of the length, at least, of 
the peduncle of the lower, and the hooks of the end of the 
feet entire. ( Aselle d'eau douce , Geoff. Idotea ciquatica. 
Fab.) 
Oniscoda, Latr., 
Or janira of Hr. Leach, differ from asellus in the approxima- 
tion of their eyes, their upper antennas being shorter than 
the peduncle of the lower, and in the knobs of the tarsi, 
which are bifid. {Janira maculosa, Leach.) 
