VI FAMILIES OF CYCLOMETOPA IgI 
The carapace is sub-circular, and the rostrum short and toothed. 
Atelecyclus, European seas. 
Fam. 3. Cancridae.—The carapace is broadly oval or hexa- 
gonal, and the flagella of the second antennae are short and not 
hairy as in the foregoing. The first antennae fold lengthwise. 
Carcinus maenas on English and North European coasts. This 
crab has become naturalised in some unexplained manner in 
Port Phillip, Melbourne. Cancer in North Atlantic, North 
Pacific, and along the west coast of America into the Antarctic 
regions. C. pagurus is the British Edible Crab. 
Fam. 4. Portunidae.—The legs are flattened and adapted for 
swimming. The first 
antennae fold back 
transversely. — Portu- 
nus, Atlantic and 
Mediterranean. Nep- 
tunus, Indo - Pacific. 
Callinectes, C. sapidus, 
the edible blue Crab 
of the Atlantic coasts 
of America. Lupa 
@iigs U3 1): 
Fam. 5. Xanth- 
idae—The first an- 
tennae fold  trans- 
versely, but the legs 
are not adapted for swimming; the body is usually transversely oval. 
This family is especially characteristic of the tropical httoral, where 
it is very widely represented. Lantho, Actaea,Chlorodius, Pilumnus, 
Eriphia, with E. spinifrons, common in the Mediterranean. 
Fam. 6. Thelphusidae (Potamonidae).—iresh-water crabs, 
with the branchial region very much swollen. Thelphusa (or 
Potamon) has nearly a hundred species distributed from North 
Australia, through Asia, Japan, the Mediterranean region, and 
throughout Africa. Potamocarcinus in tropical America. 
Fig. 131.—Dorsal view of Lupa hastata, x 1. (From an 
original drawing prepared for Professor Weldon.) 
Tribe 4. Oxyrhyncha. 
This section includes the Spider-crabs and related genera, 
in which the carapace is triangular, with the apex in front 
