Abnormal Appendages in Crabs. 403 



an angle of rather less than 60'^ with that of the normal 

 carpus. 



Articulating with the secondary carpiis is a chela measuring 

 26 mm, in length along the lower edge. It approaches the 

 normal chela of the species in form and colour, except that 

 the palmar portion is narrowed just beyond the base, with 

 its upper and lower edges concave, the lower edge becoming 

 strongly convex at the base of the immovable finger. The 

 granulated ridges on the palm are feebly developed, but all 

 those present in the normal chela can be recognized ; espe- 

 cially noteworthy is the inner ridge of the upper margin, 

 which ends in a strong spine overhanging the base of the 

 dactylus, as in the normal chela, and, together with the carpal 

 spine, shows* at once that we have to do with a left, not with 

 a right, chela. The fingers have a slight curvature inwards, 



Abnormal cheliped of Portunus piiher, from above. Xatural size. 



the dactylus, in addition, being angularly bent at a short 

 distance above the base ; except for this and for some other 

 small irregularities they resemble in form, sculpture, and 

 colour those of the normal chela. 



In other respects the crab appears to be quite normal, 

 except that three of the walking-legs are just beginning to 

 regenerate after autotomy and that the penultimate antero- 

 lateral tooth on the left side of the carapace is broken or 

 worn away at the tip. On folding the left cheliped against 

 the carapace it is seen that the inner spine of the secondary 

 carpus abuts against this tooth. 



This case seems to be excluded from all those categories 

 into which, as Bateson showed, the vast majority of cases of 

 extra appendages in Arthropods naturally fall. The extra 

 chela shows no trace of duplicity, as if it represented a pair 



