CHAP, xxi.] SECONDARY SYMMETRY : CRUSTACEA. 



/ 



533 



820. 

 1821, 



822. 



I U 



Fig. 187. I. Cancer pagurus, No. 820, right chela. Specimen in Coll. Surg. 

 Mus. II. Astacus leptodactylus, left chela, after Karoli. 



Cancer pagurus : somewhat similar case in rt. chela (Fig. 187, 

 I) ; but here the normal, R, stands in its normal place. In Coll. 

 Surg. Mus. 



Homarus americanus : dactylopodite only of right chela 

 preserved. It is bent sharply downwards, out of the plane of 

 the " hand," and bears upon its upper surface two pairs of blunt, 

 toothed processes [probably being rudiments of two pairs of extra 

 dactylopodites]. Faxon, I.e., p. 261, PL II. fig. 1. 



Homarus americanus : dactylopodite (a) bent upwards and 

 outwards, crossing index without meeting it (Fig. 188). From 

 the smooth border of dactylopodite arise two toothed processes 



Fig. 188. Homarus americanus, No. 822, left chela, a, normal point of 

 dactylopodite. b, c, extra points. (After Faxon.) 



(b and c) curving towards index. [I take it that this is some- 

 thing like the cases of Position A in Insects (p. 481) but from 

 the original figure the relations cannot be quite decided.] Faxon, 

 I.e., p. 260, PI. I. fig. 15. 



