314 ASELLIDE. 
ISOPODA. ASELLIDA. 
NORMALIA. 
Genus. JIRA. (Leach.) 
Generic character. Upper antennew very short. Lower 
antennse more than half the length of the animal. Legs uni- 
form, slender. Pleon coalesced into one segment, furnished with 
two minute subterminal uropoda. Pleopoda or branchial appen- 
dages covered bya large plate occupying the entire under surface 
of the pleon. Dactyla biunguiculate. 
Tue small flattened species, which is the type of the 
present genus, is distinguished from the allied genera by 
the minute upper antennze and terminal appendages to 
the tail, the claws 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 antennz not having their basal joints 
concealed, but arising within the emargination, The 
upper or inner antennze 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 
