160 CLASS CRUSTACEA. 



Gecarcinus, Latr., 



Whose four antennae are covered by the hood ; the second and 

 third articulation of the exterior jaw-feet are large, flatted, as 

 it were foliaceous, arched, and leaving a vacancy between 

 them on the internal side ; or the last of these articulations is 

 in the form of a curvilinear triangle, obtuse at the summit. It 

 reaches the hood, and covers the three following articulations 

 (4, 5, and 6.) Cancer ruricola, Lin. 



Sometimes the testa is almost square, subisometrical, or but 

 little broader than long, flatted, with the front diminished in 

 almost its entire breadth ; the ocular pedicles are short, and 

 inserted at the lateral anterior angles ; the two ordinary divi- 

 sions of the intermediate antennce are very distinct; the ex- 

 ternal jaw-feet are separated internally, and form by this 

 separation an angular vacancy ; their third articulation is 

 almost as long as broad ; the claws are short and thick, and 

 the other feet are very much flatted ; the fourth pair, and then 

 the third, are longer than the others ; the tarsi are spinous. 



Plagusia, Latr.^ 



Have their middle antennae lodged in two longitudinal and 

 oblique fissures, traversing the entire thickness of the middle 

 of the hood. P. depressa, Latr. 



They are inferior, or covered by this part in 



Grapsus, Lam. 



Their testa is a little wider in front than behind, or at least 

 not more narrow, while in plagusia it widens a little from front 

 to rear. Grapsus rarius, Latr. 



Our fourth section, Orbiculata, has the testa either sub- 



