DECAPOD A. ASTACIDsE. 



MACROURA. 



GENUS HOMARUS. EDW. 



CANCER. Linn. 



CANCER (Astacus.) Penn. 



ASTACUS. Fabr. Latr. Leach. 



HOMARUS. Edw. 



Generic Character. External antenna placed above and to the 

 outer side of the internal; the laminar appendage dentiform, 

 dilated on the inner side,, scarcely covering the penultimate joint 

 of the peduncle. Internal antennce with the peduncle nearly as 

 long as that of the external. External pedipalps pediform, ex- 

 tending forwards beyond the peduncles of the antennae. Anterior 

 legs very robust, unequal; the larger with the fingers strongly 

 tuberculated on the grasping edge, the smaller merely toothed ; 

 second and third pairs didactyle; fourth and fifth pairs mono- 

 dactyle. Carapace nearly cylindrical, the rostrum armed on each 

 side with three or four teeth. Thorax with the last joint im- 

 moveably connected with the preceding one. Abdomen nearly 

 cylindrical, the segments terminating laterally in a large flat 

 triangular process; terminal segment (or central lamina of the 

 tail) armed with a tooth on each side near the extremity. Tail, 

 with the exterior lamina divided transversely, about one-third 

 from the extremity, with a distinct rnoveable joint. 



R 



