4 
3rd pair of maxillipeds, for the entrance of the water into the branchial cavities. 
On the carapace, 4 regions may be more or less distinctly distinguished, 2 suc¬ 
cessive median, and 2 lateral. Of these regions the lateral ones occupy by far the 
greater part of the carapace, and represent the branchial regions. They extend 
throughout the whole length and depth of the carapace, and draw closer together 
dorsally, so as to leave only a narrow space in the middle, by which the 2 median 
regions are connected. Of these the anterior may be termed the gastric region, 
as beneath it the stomachal part of the intestine is located. Anteriorly, this re¬ 
gion is very sharply defined by the above-mentioned diverging fissures encompas¬ 
sing the frontal lobe; posteriorly, it gradually contracts, passing without any 
distinct limit, at about the middle of the carapace, into the posterior region. 
This region occupies the posterior part of the dorsal face of the carapace, and 
gradually widens somewhat behind. It may be termed the cardiac region, be¬ 
cause at any rate the anterior part of the heart, with the great artery-stems, lies be¬ 
neath its posterior part. 
The exposed part of the trunk, as stated above, is generally composed of 5 
segments, the 1st of which, however, is sometimes (Cuma) almost wholly concealed, 
in which case, only 4 such segments appear behind the carapace. Of the segments, 
the 2nd and 3rd are the largest, and are, as a rule, firmly connected, whereas 
the 2 posterior segments are generally separated by thin-skinned interspaces, al¬ 
lowing them comparative freedom of movement. The epimeral plates are easily 
observable in most of the forms, and in the adult males generally appear more 
extant than in the females. In the last segment they sometimes project posteriorly 
to spine-like processes. 
The tail is narrow cylindric in form, very flexible, and always composed of 
6 sharply defined segments, of which the penultimate is the longest. The epime¬ 
ral plates are wanting in the female, whereas in the adult male they are more 
or less distinct in those segments which carry pleopoda. The last segment is 
slightly dilated distally, and carries at the tip 2 diverging biramous appendages, 
the uropoda, and in some cases a median piece between them, the telson. 
The integuments, in the greater number of the forms, are rather hard and 
brittle, being strongly incrusted, and they exhibit a closely reticulated, or squamous 
structure. In some cases they project in spine-like processes (especially on the 
carapace), or are thickly covered with strong hairs; but in other cases, they ap¬ 
pear perfectly smooth. 
The eyes, when present, are, as a rule, united in a single organ, which 
occupies the end of the bell-shaped frontal lobe, appearing generally as a small 
nodule, just above the base of the pseudorostral prominence Only in the genus 
