VI FAMILIES OF CARIDEA 163 
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 
hes 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 pre- 
ceding. It is also a characteristic deep-sea family. Acanthe- 
phyra, Hymenodora, Nematocarcinus, ete. 
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 (Z’roglocaris, Xiphocaris from 
Australia and the Malay Islands, Atyephyra from 8S. 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.\—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 Mediter- 
ranean they penetrate very rarely into colder seas. 
1 Coutiére, Fauna and Geogr. Maldive and Laccadive Archipelagos, ii., 1905, p. 852. 
