LIGIA. 443 
The outer antenne are of considerable length, con- 
sisting of a strong five-jointed peduncle, of which the 
joints gradually increase in length, followed by a multi- 
articulate flagellum, which, in our only British species, 
contains thirteen or fourteen articuli, the last being ex- 
tremely minute; but in some of the exotic species as 
many as thirty. The inner antenne are very minute, 
flattened, and three-jointed. They are inserted close 
together, just above the clypeus, and are not longer than 
the basal joint of the outer pair. 
The body is oval and moderately convex, with the 
seven segments well developed, the lateral portions, con- 
sisting of the coxe, or first joint of the legs soldered to 
the segments, being indicated by slightly impressed lines, 
nearly parallel with the lateral margins, and being nearly 
equally developed in all the segments. The tail consists 
of six segments, of which the two anterior are distinct 
on the middle of the back, but with the sides shortened 
and concealed by the posterior direction of the lateral 
extremity of the preceding segment of the body. The 
third and two following segments of the tail are free, and 
have their posterior angles acute; whilst the terminal 
segment has the posterior margin rounded, and on each 
side the posterior angle is produced to a tooth. The ter- 
minal pair of appendages are posteriorly exserted, and 
are more or less elongated in various species. The basal 
joint is truncated at its extremity, and furnished with a 
pair of elongated cylindrical rami of nearly equal length 
and size, the inner one terminated by a solitary strong 
hair. 
The species are extremely active. ‘They are very com- 
mon on rocks just above high-water mark, hiding them- 
selves in crevices of the rock and beneath stones with 
great agility. 
