ORDER DECAPODA. 183 



position of the eyes, and some other parts, Dr. Leach has es- 

 tablished three genera: 1st. ScYLLARUS with the thorax as 

 long or longer than broad, without lateral incisions, and the 

 eyes always situated near its anterior angles. The last arti- 

 culation but one of the two posterior feet is unidenticulated in 

 the females. {Cancel- arctiis, Linn.) 



2nd, His Thenus has the thorax measured in front 

 broader than long, with a deep incision at each lateral edge, 

 and the eyes situated at its anterior angles. {Thenus Tndicits^ 

 Leach.) 



3rd, His Ibacus does not differ from thenus but in the po- 

 sition of the eyes, which are approximated from the origin of 

 the intermediate antennas, or much more interior. {Ibacus 

 Peronii, Leach.) 



Palinurus, Fab., 



Have the lateral antennae large, setaceous, and bristling with 

 prickles. Some of these Crustacea arrive to a very consider- 

 able size. In the species of our coasts, and probably in 

 others, the females have at the extremity of the last articulation 

 but one of the two posterior feet, a projection in the form of a 

 spur or tooth, exclusively proper to this sex. Scyllarus presents 

 the same difference. {Palinurus quadricornis, Fab.) 



The third section, that of Astactnt, Lati-., is distin- 

 guished from the preceding, by the form of the two anterior 

 feet, and often by that of the two following pair, which termi- 

 nate by a forceps with two biters, or a didactylous hand. In 

 some the last two or four are much smaller than the preced- 

 ing, which approximates them to the anomala. But the fan- 

 like fin of the extremity of the tail, and other characters 

 remove them from these last. The thorax is narrowed in 

 front, and the forehead advances more or less, in the manner 

 of a beak or pointed muzzle. 



Some Galathade^, Leach, have, as well as the preced- 



1 



