I D T M I D E A. 711 



Among sea-weed, harbour of Rio Janeiro; December, 1838. Found 

 along with Caprellas. 



Length, half an inch. Colour, brown or yellowish brown ; penult 

 joint of legs, with a black or brownish transverse band. Body a little 

 convex. Head excavate in front, and having on each side two crena- 

 tions, in the posterior of which the eyes are situated. There are two 

 tubercles on the centre of the anterior margin ; in the specimen exa- 

 mined, these tubercles were a little to the left of the centre. The 

 fourth thoracic segment is broadest and longest. The first and second 

 are triangular in outline on either side, the third and fourth poly- 

 gonal. The epimerals are also angular, and may be seen from above 

 excepting the third and fourth pairs, and the third is sometimes appa- 

 rent in an upper view. The basal joints of the legs bear three or 

 four tubercles ; none were observed on the anterior pair. The right 

 of the outer antennae was a little larger than the left. 



Family CH^ETILIDiE. 



The sixth pair of legs, in the only species of this family discovered, 

 terminates in a very long, bristle-like extremity, which consists of 

 numerous joints ; it is twice as long as the body. The seventh pair 

 is similar in being without the usual claw, and has a multiarticulate 

 extremity, but is quite short. The antennae of the first pair are 

 situated over (and not inside of) those of the second pair. 



The Chaetiliae belong to quite a distinct group from the preceding 

 Idotaeidea. It is doubtful, however, whether the group may not rest 

 for its distinctions more properly on other characters than those men- 

 tioned. This cannot be fully known until other related genera are 

 discovered. 



Genus CH^TILIA. 

 AntenncB lmce super 2das insitce et longiores; inferiwes (2dce) flagello 









