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 tlie 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 maxilla3 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 coxse, and the ring is 

 continued beneath, terminating 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. 



