240 A HISTORY OF RECENT CRUSTACEA 
There appear to be only two or three genera belonging 
to this family, and those confined to fresh water. 
Atya, Leach, 1817, was called Atys in 1815, but the 
name was pre-occupied. It has in the first two pairs of 
trunk-legs the chele fringed with long hairs; the third 
pair are large and long, the fourth and fifth robust, shorter 
than the third. The genus Atyoida, Randall, 1839, is by 
Spence Bate considered a synonym of Atya, and he also 
seems to contemplate the possibility that species of Caridinua, 
Milne-Edwards, 1837, may prove to be young stages of Atyu. 
The latter genus includes several species, distributed in 
the islands of the Pacific and Atlantic, in New Zealand, and 
Mexico. Atya sulcatipes, Newport (see Plate X.), is found 
in the Cape Verde Islands, and is perhaps only a variety 
of the older Atya scabra, Leach, while Atya serrata, Spence 
Bate, also from the Cape Verde Islands, is said to exhibit 
only slight and unimportant differences from Atya bisulcata 
(Randall), which is found in the Sandwich Islands. The 
structure of the first two pairs of trunk-legs in this genus 
is not a little remarkable. The first joint has a tuft of 
long hairs set on a tubercle, and has a rudiment of an 
epipodal plate fringed with hairs; the third and fourth 
joints have hairy fringes ; the tifth joint or wrist is short 
and crescent-shaped ; but the chief peculiarity is in the 
arrangement of the sixth and seventh joints, which together 
have something of the form of a horseshoe magnet, the hand 
being articulated near its centre with the lower angle of the 
wrist, and both hand and finger have their flattened ends 
furnished with long finely ciliated hairs. ‘ When the hand 
is opened,’ according to Fritz Miiller, ‘the hairs upon the 
margin of the fingers spread like a fan, gather and retain 
fine mud ; when the hand is closed these hairs close round 
the mud and compress it into a pellet which is passed into 
the mouth, and so the animal lives on the small organiz 
substances that exist in the mud, which it collects with 
great rapidity.’ According to Mr. Spence Bate himself, 
‘these animals, of which the male is smaller than the 
female, as is frequently the case when they are not pro- 
vided with offensive weapons, are only known to inhabit 
