DECAPODA. TUALASSINADjE- 



MACROUKA. 



GENUS OALLIANASSA. Leach. 



Cancer (Astacus). Montagu. 

 Callianassa. Leach, Edwards. 



Generic Character. — Atitennce inserted in nearly the same ho- 

 rizontal line. External antennce. with an elongated peduncle, 

 and without any moveable scale at the base. Internal antennce 

 with an elongate, rather thick, cylindrical peduncle, terminating 

 in two setse scarcely longer than the peduncle itself. External 

 pedipalps with the second and third joints very broad, consti- 

 tuting when in contact a broad oval disk, and terminating in a 

 small seta formed of the last three joints : there is no palp. 

 Anterior feet very unequal, one, generally the right, being ex- 

 tremely large ; the first three joints of moderate size ; the arm 

 furnished with a strong, hooked process on its outer margin ; the 

 wrist and hand enormously developed, the former attached to 

 the arm by a narrow neck ; these two joints are of nearly the 

 same dimensions, and united by a straight line : second pair 

 small, didactyle ; third pair monodactyle, the penultimate joint 

 much dilated ; fourth pair simple ; fifth pair subdidactyle. Cara- 

 pace small, without any rostrum. Abdomen very long : the first 

 five segments broad ; the sixth abruptly narrower ; the seventh 

 triangular. 



This genus may be considered as a fair type of the 

 remarlcable family to which it belongs, and which con- 

 stitutes the true fossorial group of the Macroura. The 

 wdiole of them burrow in the mud or sand, and remain 

 generally concealed in these retreats. They are cha- 



