MYSIDEA. 669 



small spheroidal organ in the bases of the inner antennae, shown to 

 correspond to ears, by Huxley, are very distinct. 



The carapax following the antennary segment is very small and 

 narrow, and hardly covers the bases of the legs. In a vertical view, 

 it is widest in front, the form being narrow ovate, and on each 

 shoulder there is an acute spine ; posteriorly it narrows, so as not to 

 be wider than the abdomen where it meets it, and in this respect the 

 genus is like Sceletina. In a lateral view, the portion of the cephalo- 

 thorax covered by the carapax is widest posteriorly. At its anterior 

 part there is a buccal prominence, containing a pair of mandibles, and 

 followed by two pairs of maxillae and one of maxillipeds. The man- 

 dibles are without palpi, and have a dentate summit. The maxillae 

 are represented on Plate 44, figures 9 e, Qf. The following organs are 

 five pairs of thoracic legs, the first pair of which might as properly be 

 called maxillipeds, as they are folded back, at the third articulation, 

 .upon themselves, and thus differ from the true legs, which are all 

 nearly straight, and project forward when in their natural position. 

 These legs consist of five to six joints, and have two divergent series 

 of shortish setae ranging along their length; they are without a 

 palpus, or it is obsolescent. The first pair has a fouette, which ex- 

 tends back under the carapax, and is kept in constant rapid motion, 

 and has distinctly six joints ; the following three pairs appear to have 

 but five joints, the claw or tarsus being absent ; the last pair has a 

 very short claw. The last two pairs are the longest, next the second, 

 and next the third pair, this being much shorter than either of those 

 adjoining. 



Counting the cephalothoracic organs that are present in these ani- 

 mals, we find only twelve pairs, as follows : 



1. The eyes. 



2, 3. The antennae, two pairs. 



4. The mandibles. 



5, 6. The maxilke, two pairs. 



7. The outer maxillipeds. 



8, 9, 10, 11, 12. Five pairs of legs. 



It appears, therefore, that there are normally two pairs obsolete, 

 no trace of which, either through a tubercle, or any other sign, is 

 present. There is, however, in the posterior part of the thorax in 

 males a glassy, reddish-coloured organ, of an eardrop form, as shown in 



168 



