MUTATIONS IN CRUSTACEA OP THE FAMILY ATYID.1-:. 787 



family the characters used as distinctive of the genera are 

 chiefly drawn from the modifications of the chelipeds, nnd 

 some of these may now be considered in fuller detail. 



In the very numerous species of the genus Caridina (Text- 

 fig. 2) the chela? themselves do not differ greatly, except in 

 carrying brushes of seta?, from the typical form found in many 

 other Decapods. The dactylus (d) or terminal segment of 

 the limb, forming the "movable finger," is opposed to a 

 thumb-like process (" immovable finger ") of the penultimate 



Caridiiia mlotica var. 1. 2. first and second clielipeds. 

 c, carpus ; d., dactylus ; jy.. palmar portion of propodus. x 40 

 - From a specimen collected liy Dr. W. A. Cunnington in the 

 Victoria Nyanza. 



segment or propodus. The proximal part of the propodus, 

 expanded to contain the muscles moving the dactylus, forms 

 what is known as the "palm" (p.) of the chela. In Caridina 

 the two pairs of chelipeds differ in the form of the segment 

 which supports the propodus, the " wrist'"' or carpus {<-.). In 

 the second pair it is more or less elongated and slender, and 

 the propodus articulates with its distal end; in the first pair, 

 on the other hand, it is short and broad, its distal margin is 

 more or less concave (cf. Text-fig. 2, 1, and I'ext-fig. 4, .4'), 

 and the propodus articulates with its lower corner. 



VOL. 55, PART 4. NEW SERIES. 53 



