314 ASELLID.E. 



ISOPODA. A SELLIDjE. 



NORMALIA. 



Genus. J^RA. {Leach.) 



Generic character. Upper antennje very short. Lower 

 auteiinse more than half the length of the animal. Legs uni- 

 form, slender. Pleou coalesced into one segment, furnished with 

 two minute subterminal uropoda. Pleopoda or branchial appen- 

 dages covered by a large plate occupying the entire under surface 

 of the pleon. Dactyla biunguiculate. 



The small flattened species, which is the type of the 

 present geifus, is distinguished from the allied genera by 

 the minute upper antennae and terminal appendages to 

 the tail, the clav^^s with which the moderately long slender 

 uniform feet are furnished at the tip, and especially the 

 very remarkable structure of the under surface of the 

 tail. The body is considerably flattened, and elongate- 

 ovate (or narrow in some exotic species). The head is 

 not soldered to the following segment of the body ; its 

 sides are rounded, having, like the segments of the body 

 and the tail, a thin lateral margin. Its fore margin is 

 bi-emarginate, the antenna9 not having their basal joints 

 concealed, but arising within the emargination. The 

 upper or inner antennae are very small and four-jointed, 

 not extending to the third joint of the outer pair, which 

 are considerably more than half the length of the entire 

 animal, with the two basal joints short, the third twice 

 the length of the preceding, the fourth long and more 

 slender, but thickened towards the tip, followed by a 

 very long and slender multiarticulate flagellum. The 



