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 

 riodule, just above the base of the pseudorostral prominence. Only in the genus 



