=Tribe 4. Caridea.= The third legs are not chelate. The third maxillipedes are 4–6 jointed, the end-joint of the second maxillipede nearly always lies as a strip along the end of the joint before it, and the first maxillipedes have a lobe on the base of the exopodites. The pleura of the second abdominal segment overlap those of the first. The abdomen has a sharp bend; the branchiae are phyllobranchs. =Fam. 1. Pasiphaeidae.=—In this family the end-joint of the second maxillipedes is normally formed, and exopodites are usually present on all the thoracic limbs. Rostrum small or wanting. Rather numerous genera are known, most of which inhabit the deep sea, though a few come into the littoral zone. _Pasiphaea_ chiefly in the deep sea, _Leptochela_ in the tropical littoral zone. =Fam. 2. Acanthephyridae.=—The end-joint of the second maxillipede is modified as in other Caridea, and the rostrum is very strong and serrate, but in the presence of exopodites, and in the form of the mouth-parts, this family agrees with the preceding. It is also a characteristic deep-sea family. _Acanthephyra_, _Hymenodora_, _Nematocarcinus_, etc. =Fam. 3. Atyidae.=—This is an entirely fresh-water family, especially characteristic of the rivers and lakes of the tropics, some of the forms being exceedingly large and taking the place of the Crayfishes in these waters. Characteristic of this family is the fact that the fingers of the chelae are spoon-shaped, and carry peculiar tufts of bristles. Exopodites are present on the thoracic limbs of some of the genera (_Troglocaris_, _Xiphocaris_ from Australia and the Malay Islands, _Atyephyra_ from S. and W. Europe), but are absent in others. _Caridina_, widely spread and common in Indo-Malay and Africa; _Atya_ from West Indies, West Africa, and Pacific Islands. =Fam. 4. Alpheidae.=[137]—The exopodites are absent, and the rostrum is absent or very feeble. The chelae are powerful, and usually very asymmetrically developed. _Alpheus_ has an enormous number of species which live chiefly in the tropical seas, where they haunt especially the coral-reefs, making their homes among the coral or in sponges, etc. Although occurring in the Mediterranean they penetrate very rarely into colder seas. =Fam. 5 Psalidopodidae.=—This family, characterised by the absence of chelae on the second thoracic limbs, which carry instead a terminal brush of hairs, and by the rudimentary condition of the eyes, is represented by the genus _Psalidopus_ from the deep waters of the Indian Ocean. =Fam. 6. Pandalidae.=—The first thoracic limb is without chelae, only six-jointed. The rostrum is large and toothed. The genus _Pandalus_ has numerous representatives in the northern littoral, _P. annulicornis_ being one of the prawns most commonly met with in the fish-markets.