=Fam. 2. Atelecyclidae.=—Perhaps related to the foregoing. The carapace is sub-circular, and the rostrum short and toothed. _Atelecyclus_, European seas. =Fam. 3. Cancridae.=—The carapace is broadly oval or hexagonal, 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. [Illustration: FIG. 131.—Dorsal view of _Lupa hastata_, × 1. (From an original drawing prepared for Professor Weldon.) ] =Fam. 4. Portunidae.=—The legs are flattened and adapted for swimming. The first antennae fold back transversely. _Portunus_, Atlantic and Mediterranean. _Neptunus_, Indo-Pacific. _Callinectes_, _C. sapidus_, the edible blue Crab of the Atlantic coasts of America. _Lupa_ (Fig. 131). =Fam. 5. Xanthidae.=—The first antennae fold transversely, but the legs are not adapted for swimming; the body is usually transversely oval. This family is especially characteristic of the tropical littoral, where it is very widely represented. _Xantho_, _Actaea_, _Chlorodius_, _Pilumnus_, _Eriphia_, with _E. spinifrons_, common in the Mediterranean. =Fam. 6. Thelphusidae (Potamonidae).=—Fresh-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. =Tribe 4. Oxyrhyncha.= This section includes the Spider-crabs and related genera, in which the carapace is triangular, with the apex in front formed by a sharply-pointed rostrum. There are two chief series, the one comprising the Spider-crabs, with much elongated walking legs, _e.g._ the huge _Maia squinado_ of European seas, the yet more enormous _Macrocheira kämpferi_ from Japan, supposed to be the largest Crustacean in existence, and sometimes spanning from outstretched chela to chela as much as eleven feet, and the smaller forms, such as _Inachus_, _Hyas_, and _Stenorhynchus_, which are so common in moderate depths off the English coasts. The other series is represented by genera like _Lambrus_ (Fig. 133), in which the legs are not much elongated, but the chelipedes are enormous.