10 AURIVILLIUS, A NEW GENUS OF HARPACTICIDA. 
two sete, the outer having also two sete at the apex and 
three on the outer margin. 
Nhe inner? branch tm) the, dfemalest(RI4riIrITIstGY TES 
five sete, the two inner shorter and, as it were, flattened 
towards the apex; outer branch having three longer and three 
very short sete. 
The first abdominal segment of the male has on the 
ventral surface two elevations (Pl. II. Fig. 5.), separated by a 
median furrow, but coherent at the base, each bearing one 
seta, a little curved, at the apex. They resemble very 
much the inner branches of the fifth pair of feet, and it may 
be that they are a still more rudimentary pair of feet. On the 
first abdominal segment of the female, the sexual apertures (Pl. 
II. Fig. 7.) appear in the form of two oval recesses, meeting in 
the middle. The outer part of their anterior margin has 
a small tubercular lamina, with two sete; the middle of the 
same margin, with a conical process. A little behind the sexual 
apertures there is, in a cavity situated in the middle line of 
the ventral surface, a small semicircular lamina, ciliated at 
its margin. Övisacs two, with about twenty eggs in each. 
If now the sexual differences are recapitulated, it 18 
found that the male differs from the female by 1:0o the struc- 
ture of the anterior antenne, 2:o the shape of the sete at 
the inner branch of the second pair of feet, 3:o the seta at 
the outer margin of the outer branch in the third and fourth 
pairs of feet, 4:o the more rudimentary state of the fifth 
pair of feet, 5:o the distinctly marked first and second ab- 
dominal segments, 6:0 the laminar appendages on the first 
abdominal segment. 
B. Development. 
The "new-hatched young is a Nauplius having the body 
scarcely more than three quarters as long as broad. Al- 
though it be possible that in this stage of development the 
young moults several times, yet I have not met with more 
than two slightly differing forms. One, the smaller, prob- 
ably represents the animal when leaving the egg, and differs 
from the larger by having but one rudimentary pair of feet 
at the posterior end of the body and one spinous seta on 
