CHAP. XXL] SECONDARY SYMMETRY : CRUSTACEA. 



529 



813. Astacus fluviatilis : about 3 years old according to Sou- 

 BEIRAN'S (Comp. Rend. 1865, LX. p. 1249) account. Right chela ap- 

 parently deformed by injury or disease. Left chela had all normal 



m 



FIG. 182. I and II. Eriphia spinifrons, No. 812. I. A view of the left chela. 

 II. An enlarged view of the extra parts from the other side. LD, LI, normal left 

 dactylopodite and index. R'D, L'D, right and left extra dactylopodites. RI, L'l, 

 right and left extra indices not separated from each other. (After Herklots.) 



III. Cheliped of Homants americanus, No. 814. (After Faxon.) D, I. normal 

 dactylopodite and index. D', D", extra dactylopodites. I', I", perhaps an 

 indication of double extra indices. 



IV. Astacus ttuciatilis, No. 813, left chela. L, normal left dactylopodite. 

 R'D, L'D, right and left extra dactylopodites. L'l+R'I, left and right extra 

 indices not separated from each other. (After Maggi.) 



parts and in addition the structure shewn in Fig. 182, IV upon the 

 pollex-border of propodite. Here was a boss, separated by a 

 groove. It was observed that the structure was that of a rt. 

 and 1. dactylopodite working upon a double index [as in last 

 case]. Structure of muscles, fully described, was also in agree- 

 ment with the view that the extra parts were a complementary 



B. 34 



