DESCRIPTION OF AN ABNORMAL LOBSTER CHELIPED. 259 



morphological plane. This is illustrated in Fig. 5. This''figure 

 represents diagrammatically a cross section through the index 

 and dactyl of a normal claw from the left side of a lobster, 

 viewed from the position of the distal end of the appendage. 

 The posterior side of the claw, which is more darkly pigmented 

 in the living lobster, is here shaded, while the ventral side is 

 left clear. The primary morphological relations, as they would 

 obtain if the appendage were extended laterally in a horizontal 



Fig. 5. Diagram to illustrate effects of torsion in a normal left chela, 

 primary morphological position; II., position as a result of torsion. 



I., 



plane and there were no torsion, are shown in the position marked 

 I, where the plane passing through the index {IL) and dactyl 

 {DL) is vertical. Due to torsion, however, the claw is rotated 

 anteiiorly^ nearly 90° (probably ordinarily 75°-8o°; for con- 

 venience, we may call it 80°), so that its plane approximates the 

 horizontal, as shown in position II. The dactyl thus lies an- 

 teriorly, while the posterior surface (shaded) is uppermost. By 

 a bending of the leg now, however, the claws may be brought 



^ By "rotated anteriorly" it is meant that the dorsal side has rotated over in 

 the anterior direction. 



