G. M. Tuomson.—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 sete or spines. In 
the second pair both carpus and propodos are elongated, and their finely- 
serrated palms are almost destitute of sete. The 1st and 2nd pereiopoda 
are long, slender, and sparingly furnished with hairs. The 8rd 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 sete on the front 
margin. The last pair 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 
antenne as in the male. The anterior antenne 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 sete are developed on its outer margin; the flagellum is 
2-jointed, but the last joint in mature specimens appears to be sometimes 
divided into two. The posterior antenne are quite absent, as are also the 
mandibular palps. The length of the body is from 1 to 1} inch. The 
animal is absolutely transparent and glass-like, 
