ORDER ISOPODA. 223 



Arcturus, Latr., 



Are very remarkable for the form of the second and third feet, 

 which are directed forward, and terminate by a long barbed 

 articulation, and imperfect, or but slightly unguiculated. 

 The anterior two are applied on the mouth, and unguicu- 

 lated. The last six are strong, ambulatory, thrown back- 

 wards, and bidenticulated at their extremity. In the relation 

 of the length of their antennae, and the form of the body, they 

 approach Stenosoma. {Arcturus tuherculatiis, Lat.) 



The fifth section (Asellota, Lat.) presents us with isopods 

 Math four very apparent antennse, disposed on two lines, seta- 

 ceous, terminated by a pluri-articulate stem ; two mandibles, 

 four jaws, usually covered by a sort of lip, formed by the first 

 jaw-feet; vesicular gills disposed in pairs, covered by two 

 longitudinal and biarticulate leaflets, but free ; a tail formed 

 of a single segment, without lateral fins, but with two bifid 

 stylets, or two very short appendages, in the form of tuber- 

 cles, at the middle of its posterior edge. Some other appen- 

 dages, in the form of lamina?, situated at its inferior base, 

 more numerous in the males, distinguish the sexes. 



ASELLUS, Geoff., 



Have two bifid stylets at the posterior extremity of the body, 

 the eyes apart, the upper autennge of the length, at least, of 

 the peduncle of the lower, and the hooks of the end of the 

 feet entire. {Aselle cTeau douce, Geoff. Idotea aquatica, 

 Fab.) 



Oniscoda, Latr., 



Or janira of Dr. Leach, differ from asellus in the approxima- 

 tion of their eyes, their upper antennae being shorter than 

 the peduncle of the lower, and in the knobs of the tarsi, 

 which are bifid. {Janira maculosa, Leach.) 



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