182 CLASS CRUSTACEA. 



number. The two middle antennse are never terminated but 

 by two threads, and generally shorter than their peduncle, or 

 scarcely longer. The external leaf of the natatory appen- 

 dages of the last segment of the tail but one, is never divided 

 by a transverse suture. 



Our second section, LocusTA, thus designated from the 

 word locasta, applied by the Latins to the most remarkable 

 Crustacea of this division, from which comes the French word 

 Imigouste, have always but four pair of false feet. The pos- 

 terior extremity of the fin terminating the tail is always almost 

 membranaceous, or less solid than the rest. The peduncle of 

 the middle antennae is always longer than the two threads of 

 the end, and more or less folded or bent; the lateral ones are 

 never accompanied with scales : sometimes they are reduced 

 to a single pedicle, which is dilated, very much flatted, and in 

 the formof a crest; sometimes they are large, long, going into 

 a point, and entirely bristling with prickles. All the feet are 

 almost similar, and go into a point at the end ; the first two 

 are simply a little stronger. Their penult articulation, and that 

 of the two last, is at most unidenticulated, but without form- 

 ing with the last a hand perfectly didactylous. The pectoral 

 space comprised between the feet is triangular. The thorax 

 is almost square or subcylindrical, without any frontal prolon- 

 gation, in the manner of a pointed bill or lance. 



SCYLLAEUS, Fah., 



Present, in the form of their lateral antennae, a character al- 

 together unusual ; the stem is wanting, and the articulations 

 of the peduncle, very much dilated transversely, form a large 

 crest, flatted, horizontal, and more or less denticulated. 



The external branch of the subcaudal appendages is ter- 

 minated by a leaf, but the internal, in some males, only shows 

 itself in the form of a tooth. 



According to the proportions and form of the thorax, the 



