186 CLASS CRUSTACEA. 



and which a single subgenus excepted (gehia) have the four 

 or six anterior feet terminated by a didactylous hand. 



Their tail is always extended ; their two posterior feet are 

 never much more slender than the preceding, nor folded. 

 The peduncle of the lateral antennae is often accompanied by 

 a shell. 



Those whose first four feet at most are terminated by two 

 lingers, whose lateral antennae never have a shell or scale at 

 the base, and in which the exterior leaf of the lateral fins of 

 the end of the tail presents no transverse suture, will form a 

 first subdivision. Their feet for the most part are ciliate or 

 hairy. 



Sometimes the index, or immoveable finger (formed by a 

 projection of the last articulation but one,) of the claws, is 

 very sensibly shorter than the thumb, or mobile finger, and 

 forms only a simple tooth. 



Gebia, Leach, 



Approach the preceding subgenera, in that the two anterior 



feet alone are didactylous. The leaves of the lateral fins of 



the end of the tail, proceed widening from their base to their 



extremity, and have longitudinal crests. The intermediate 



piece, or the last segment of the tail, is almost square. [Gehia 



stellata. Leach.) 



Thalassina, Lair., 



Have the four anterior feet terminated by two toes or fingers, 

 the leaves of the lateral fins of the end of the tail nan-ow and 

 elongated, without crests ; and the last segment of this tail, 

 or the intermediate piece, in an elongated triangle. (Thalas- 

 sina scorpionides, Latr.) 



Sometimes the four anterior feet, or the two first and one of 

 the second, are terminated by two elongated fingers, forming 

 the forceps completely. 



