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. 



Attja, Leach, 1817, was called Atys in 1815, but the 

 name was pre-occupied. It has in the first two pairs of 

 trunk-legs the chelae 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 Caridina^ 

 Milne-Edwards, 1837, may prove to be young stages of Atya. 

 The latter genus includes several species, distributed in 

 the islands of the Pacific and Atlantic, in Neiv Zealand, and 

 Mexico. Atya sidcatipes, Newport (see Plate X.), is found 

 in the Cape Verde Islands, and is perhaps only a variety 

 of the older Atya scahra, Leach, while Atya serrata^ Spence 

 Bate, also from the Cape Verde Islands, is said to exhibit 

 only slight and unimportant differences from Atyahisidcata 

 (Kandall), 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 fifth 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 liave 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 organij 

 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 



