MUSEUM OF COMPAEATIVE ZOOLOGY. 259 



its toothed margin. One of these (b) seems to be developed in order to 

 recover the prehensile power which was lost by the distortion of the 

 dactylus. The other (c) is broken off near its tip, but corresponds to 

 the process c described in the next figure. 



There is another dactylus in the collection quite similar to this. 



Plate I. Fig. 8 (right chela). — This deformity belongs to the same 

 category as the one represented by the last figure. The dactylus (a) is 

 curved strongly away from the index, and lengthened. At d is the scar 

 resulting from the wound that probably caused the curvature of the dac- 

 tylus. An outgrowth (b) provided with teeth, and meeting the thumb 

 when the claw is closed, replaces functionally the distorted extremity of 

 the dactylus. In addition to this a second process (c) projects at a 

 right angle with the deflected part of the dactylus. This process pre- 

 sents a line of teeth opposite to those on a. My reason for considering 

 a rather than b to be the end of the original dactylus, and b and c to be 

 secondary outgrowths, comes from the arrangement of the punctures 

 and the stria) on the cuticle of these parts, which seem clearly to show 

 that b and c are the newer portions. 



Plate I. Fig. 9 (right chela). — The index here is split into two parts. 

 The outer (a) is toothed on its inner border. The inner (b, c) is toothed 

 on both margins, and shows a tendency to divide at the end. The lines 

 on the cuticle show that a is the original index, and b, c, a secondary 

 process developed from it. The dactylus does not meet the index when 

 closed. 



Plate. I. Fig. 10 (right chela). — The dactylus is abnormally short 

 and curved, and its proximal half produced into a large roundish plate, 

 toothed on its margin, only the basal part of which closes against the 

 index. 



Plate I. Fig. 11 (left chela). — A large triangular crest, directed out- 

 ward and forward from the middle of the outer margin of the penulti- 

 mate segment. This crest-like process has a strong cui've downward. 



There are several claws similar to this in the collection. 



Plate I. Fig. 12 (right chela). — The inner border of the hand is dis- 

 torted by a wound (d) which has resulted in the outgrowth of a simple, 

 blunt, movably-jointed segment (a'), which evidently represents an abor- 

 tive supernumerary dactylus. On its upper side (the figure shows the 

 lower surface), near the articulation with the hand, is the small spine 

 characteristic of the normal dactylus. The abnormal finger moves in a 

 plane at right angles to the plane of motion of the normal dactylus. 



There is another specimen in the collection similar to this, — a left 



