ANIMALIA ARTICULATA. 115 



foot-jaws wide apart, leaving exposed a portion of the interior 

 of the mouth. 



FAMILY OF THE MACROURA. 



Tail well developed, generally longer than the cephalo- 

 thoracic portion of the body, extending behind and employed 

 in natation ; it has always beneath it lamellous false feet, and 

 at its extremity a fin in the form of a fan. Four remarkable 

 genera. 



GENUS PAGURUS, Fabr. Hermit Crabs. 



Body elongated; tail extended, at least as long as the 

 trunk ; the four last feet much shorter than the preceding ; 

 posterior part of the body entirely soft. Inhabit marine 

 shells. 



GENUS PAL.SJMON, Fabr. Prawns. 



Body of a less solid consistence than that of the other 

 Crustacea, arcuated, and, as it were, hunch-backed; the fore- 

 head prolonged into a beak-like point ; lateral antennae very 

 long ; the intermediate with three filaments ; carpus inarti- 

 culated ; second feet the longest. 



GENUS ASTACUS, Fabr. Lobster. 



The three first pairs of feet terminated by a dydactile 

 hand, the first enormous and like a forceps; tail fan-like with 

 lateral plates divided transversely. 



GENUS PALINURUS, Fab. 



Lateral antennas hairy, exceedingly long and thick; feet 

 simple ; only four pair of false feet. 



ORDER AMPHIPODA. 



Eyes sessile and immovable ; no carapax ; body composed 

 of rings ; four first foot-jaws serving for locomotion ; no pro- 

 per branchiae ; mandibles provided with a palpus; the five 

 first pairs of abdominal limbs aiding locomotion and not 

 branchial; palpi of the thoracic limbs vesicular and bran- 

 chial. Two remarkable genera. 



