182 CRUSTACEA. ISOPODA. 



Gen. 17- JANIIIA, Leach. Oniscus, Mont. 

 General characters of the preceding genus ; terminal hooks of 

 the fourteen feet bifid ; eyes pretty large ; intermediate an- 

 tennas shorter than the terminal setae of the exterior ones. 



J. maculostty Leach. Body cinereous,, spotted with brown. Coasts 

 of Britain, amongst marine plants. Lin. Trans, xi. 373. 



Gen. 18. J.ERA, Leach. 



General characters of the Aselli ; lateral appendages of the 

 tail terminated by simple tubercles ; eyes moderately large, 

 placed between the sides of the head and vertex. 



J. albifrons, Leach. Body cinereous, white in front. On marine 

 plants, and beneath stones in Devonshire, Lin. Trans, xi. 373. 



FAMILY V. IDOTEIDES. 



Branchial appendages under the post-abdomen, and covered by 

 the plates or valves of the terminal segment, longitudinal 

 and biarticulate ; four antennas in a transverse line, the la- 

 teral ones terminated in a setaceous filament ; post-abdomen 

 of three distinct segments. 



Gen. 19- IDOTEA, Fab. Oniscus, Lin. 



Body oblong or elongated, of seven transverse segments ; late- 

 ral antennae setaceous and longest ; head nearly the breadth 

 of the body, almost square ; two round compound eyes ; tail 

 very large, triarticulated, without terminal appendages cover- 

 ing the branchiae and their protecting laminae ; fourteen feet. 



I. entomon, Lat. Body truncated oval ; tail long and conical ; co- 

 lour grayish, brown above, and dirty- white mixed with brown be- 

 low; antennae nearly equal. 1^ to 2 inches long. Inhabits 

 Northern seas. B. Penn. Brit. Zool. iv. pi. 19, fig. 5. 



I. pelagica, Leach. Body linear oval ; tail rounded, the middle 

 with a very obsolete tooth ; antennae one-third the length of the 

 body. Inhabits Frith of Forth Lin. Trans, xi. 365. 



Gen. 20. STENOSOMA, Leach. Oniscus, Pen. 

 General characters of the preceding ; but with the exterior an- 

 tennae as long as the body, exclusive of the tail, and with the 

 third joint longer than the fourth ; body elongated, linear. 



S. lineare, Leach. Last segment of the tail somewhat narrowed at 

 the base, and dilated towards the apex, which is truncated and 

 notched. European seas. B Penn. Brit. Zool. iv. pi. 19, fig. 2. 



SECTION II. TERHESTRIA. 



Two intermediate antenna? very small, scarcely visible, and of 

 at most two joints ; post-abdomen of six segments, the poste- 

 rior margin of the last one with two bifid styles in some, in 

 others with four. 



