114 ANIMALIA ARTICULATA. 



domen; branchise formed of lamellse or filaments, always 

 simple and inserted in the internal paries of a special cavity 

 situated on each side of the thorax, and formed by the lateral 

 prolongation of the carapax ; heart nearly quadrilateral, situ- 

 ated in the middle of the thorax ; from this heart spring six 

 principal arteries, distributing the blood through all parts of 

 the body ; buccal apparatus extremely complicated, and com- 

 posed of a lip, small tongue, and six pairs of members, viz. 

 a pair of mandibles, two pairs of jaws, and three pairs of foot 

 jaws; five pairs of true feet, formed of six articulations; 1, 

 the coxa or hip ; 2, the femur or thigh ; 3, the tibia or leg ; 

 and the true foot, consisting of, 4, the carpus ; 5, the pollex ; 

 6, the index. Four antennae inserted between the eyes and 

 mouth ; eyes with facets, pedunculated and movable. Two 

 families. 



Explanation of Fig. A, PL 33. Respiratory apparatus of a 

 Decapoda : 1, branchiae ; 2, venous sinus ; 3, vessel carrying 

 out blood ; 4, vessels returning blood ; 5, heart ; 6, sternal 

 artery. The small arrows show the course of the blood 

 through the vessels. 



FAMILY OF THE BRACHYURA. 



Tail but little developed, hardly of any use in locomotion, 

 without false natatory feet, never terminated by a fin, in the 

 form of a fan, and doubled up under the body. Three re- 

 markable genera. 



GENUS PORTUNUS, Fabr. 



The two posterior feet terminating in fins ; shell forming 

 the segment of a circle, wider than long ; dilated before, nar- 

 rowed behind ; short ocular pedicles ; tail of the males with 

 five distinct rings, seven in the females. 



GENUS CANCER, Fabr. Crab proper. 



Posterior feet ambulatory; carapax at least once and a half 

 as wide as long, of a tolerably regular oval, and very convex 

 above ; anterior feet thick and short 



GENUS GECARCINUS. Leech. 



Shell in the form of a heart, thick, without teeth or spines; 

 pedicles of the eyes short and lodged in rounded cavities; 



