G. M. Thomson. — On new Crustaceans. 239 



long spine, against which the dactylos impinges. In the first pair the 

 carpus is short and stout, its inner surface, as well as that of the propodos, 

 is furnished with a considerable number of short stiff setae or spines. In 

 the second pair both carpus and propodos are elongated, and their finely- 

 serrated palms are almost destitute of setae. The 1st and 2nd pereiopoda 

 are long, slender, and sparingly furnished with hairs. The 3rd pair have 

 the basa finely-serrated on the lower front margin, while posteriorly they 

 are dilated into an oblong plate ; they are quite naked. In the 4th pair, 

 the basa are dilated into very broadly pear-shaped plates, while the re- 

 mainder of the limb is finely fringed with pectinate setae on the front 

 margin. The last pah are small, and have the basa slenderly pear-shaped. 

 The basa of these three pairs act as protective shields to the side of the 

 body, and the remaining joints of the limb when at rest lie folded up under 

 them. The three anterior pairs of pleopoda or swimmerets, have an oblong 

 basal joint, with two finely-setose branches. The three posterior pairs are 

 also double-branched, but are of very unequal length. The first pair have 

 the peduncle more than twice as long as the branches, both of which are 

 movable, and the inner one of which extends to the extremity of the telson. 

 The second pair only extend to the end of the peduncle of the first, and 

 have the outer joint alone movable. The third pair, which are placed at 

 the extremity of the last body-segment are also short, reaching to the end 

 of the telson, and having the outer joint alone movable. In all the pairs 

 the branches are finely-serrated on the margins, and the movable outer 

 one is always smaller than the inner. The telson is elongated, and sharply 

 pointed ; its separation from the last joint of the abdomen can be made out 

 on the ventral surface somewhat imperfectly, but from above it seems to be 

 completely anchylosed. The abdominal segments are all produced into a 

 sharp spine posteriorly. 



Female. — The sexual differences are very considerable in these animals, 

 showing themselves almost exclusively in the cephalon and its appendages. 



The head is much more inflated than in the male, being nearly globular, 

 so that the beak is more prominently shown ; the sides of the head appear 

 to be completely fused together below, so that there is no groove for the 

 antennae as in the male. The anterior antennae are much simpler than in 

 the male : the first joint is tolerably long, the second very short, while the 

 third is also straight and very much more slender than the male, while only 

 a few olfactory setae are developed on its outer margin ; the flagellmn is 

 2-jointed, but the last joint in mature specimens appears to be sometimes 

 divided into two. The posterior antennae are quite absent, as are also the 

 mandibular palps. The length of the body is from 1 to 1J inch. The 

 animal is absolutely transparent and glass-like. 



