PLATYARTHRUS. 463 
to indicate the soldering together of two joints in that 
situation. The segments of the body are moderately 
convex, with a narrow lateral margin. The legs are 
short, with the second and three following joints of 
nearly equal size, terminated by a small hook-like finger, 
having a small tooth on the inside near the middle. The 
mandibles are strongly elbowed in the middle and ter- 
minated with two compound teeth, and furnished with 
a curved and setose spine in the middle of the inner 
margin. (In our woodcut the mandible is represented 
as lying on its back.) The two pairs of maxille are very 
delicate, almost membranous, and ciliated at the tips. 
The foot-jaws are oblong, flat, and coriaceous, each 
terminated by two small quadrate lobes, which are trun- 
cated at the extremity, where they bear one or two small 
spines. 
The articulation between the posterior appendages and 
the last segment of the tail is very remarkable; the 
latter is destitute of the epimeral coxe, and the ring is 
continued beneath, termiuating abruptly on either side 
in a rounded lobe; so that the central portion of the 
body underneath is unprotected. The posterior pair of 
appendages are articulated to the anterior border of the 
inferior (sternal ?) part of the ring, a little within the ex- 
ternal lateral angle, by a well-marked ball-and-socket joint, 
so that at first sight it appears as though these appendages 
were derived from the penultimate and not from the 
terminal segment. The posterior appendages are exserted, 
the peduncular portion somewhat square, with the sides 
parallel. The outer ramus is nearly as long as the base, 
ovate, flattened, and pointed at the tip, where it is fur- 
nished with a minute filament. The inner ramus forms 
a slender filament, extending beyond the basal portion 
against the inner side: it is articulated near the base. 
