a)i osciiUuit Genus of Crustacea. 73 



The head is almost square, with the eyes prominent and nearly 

 circular ; its anterior angles are produced in front of the latter, 

 forming a deep frontal emargination, in which the interior or upper 

 pair of antenrife are inserted. The head is convex above, and ru- 

 gose. The interior antennae are not longer than the head, and 4- 

 jointed, the basal joint large, the next two short, and the fourth 

 long, cylindric, and terminated by setae. The lower antennae are 

 nearly as long as the body, robust, and 8-jointed, the first joint very 

 short, the second rather longer, with a deep external notch, the third 

 about as long as the head ; the two next are very long, each being 

 about one fourth of the whole length of the body ; the remaining 

 joints are very short, and finely serrated beneath, each being gra- 

 dually smaller, and the last being terminated by a minute acute joint. 

 The antennae are carried with a downward direction. 



The i)arts of the mouth are very minute and delicate, varying in 

 some respects from the trophi of Idotea, as figured in the great Work 

 on Egypt, pi. xii. fig. 6. The lip is transverse, rounded at the sides, 

 and emarginate in front. 



The mandibles are small, horny, broad, with several teeth, one of 

 which seems to represent the mandibular palpi of the Sphceromidce, &c. 



The interior pairs of foot-jaws are very thin, transparent, and 

 deeply ciliated, without any appendage. The second pair of these 

 organs are larger, with a terminal lobe, and a large external subarti- 

 culated appendage. The third or outer pair of foot-jaws are still 

 larger, and furnished Avith a broad palpus composed of four joints, of 

 which the second is the largest, and the fourth the smallest ; they 

 are also furnished with a large external Ijasal appendage. 



The first three segments of the body are very short, with a pro- 

 duced margin concealing the base of the legs, the first pair of which 

 is unlike all the others, and evidently seem to perform the office of 

 foot-jaws, notwithstanding their size ; indeed, from the manner in 

 which this as well as the three following pairs of legs are carried 

 over the mouth, it would seem that they are employed rather as 

 auxiliary organs of the mouth than as instruments of motion. The 

 very slender structure of these three pairs of legs, which are all formed 

 alike, and are strongly ciliated within, is also confirmatory of this 

 opinion. The first pair of legs are long, also ciliated within, the 

 ciliae arising in a double series, and being often bearded : this also 

 occurs in the second, third, and fourth pairs of legs, but only in two 

 hairs situated near the extremity of the penultimate joint. What 

 can be the cause of this peculiarity ? 



The fourth segment of the body is very long, occupying more than 

 one third of the whole length of the insect, and being perfectly cylin- 



