548 CRUSTACEA MALACOSTRACA. 



With the Catometopa is probably also allied Cymopolia Roux 

 ( = Palicus), Mediterranean and G. of Mexico. 



Tribe 5. CYCLOMETOPA. 



Carapace wide and regularly arched anteriorly ; the front not depressed 

 nor rostrate, epistome short. 



Fam. 1. Thelphusidae (Potamonidae). Carapace dilated over 'the 

 branchial regions. Fluviatile or in damp forests. Classed by some 

 authors with the Catometopa, and intermediate between these and the 

 Cancridae. Thelphusa Latr. Th. fluviatilis Latr. (Potamon edule) widely 

 distributed, S. Europe, N. Africa. The young leave the egg in the adult 

 form (Mercanti). Th. dehaanii White ascends to 2,500 ft. in Japan. 

 Paratelphusa M. Edw. Indo-Malayan. Deckenia Hilg., E. Africa and 

 Seychelles, has acquired an efferent respiratory channel similar to that of 

 the Oxystomata. 



Fam. 2. Cancridae. Carapace broad, convex, anterior margins 

 arched ; front moderately wide. Some 50 genera. Cancer L. front 

 3-toothed ; C. pagurus L. the crab of the markets, frequents holes in rocks, 

 in pairs. Pilumnus Leach. P. hirtellus (L.) British ; front projecting, 

 cephalo-thorax high arched. Pirimela Leach, P. denticulate (Montagu) 

 British. Eriphia, Latr. 



Fam. 3. Trapeziidae (Xanthidae). Carapace depressed and nearly 

 quadrilateral, antero -lateral margins entire or with 1 tooth. Small crabs 

 of warm seas. Spp. numerous in the tropics. Trapezia, Latr. ; Tetralia 

 and Quadrella, Dana. Xantho Leach. X. incisus Leach, and X. hydro- 

 philus (Herbst) British. Pseudozius, Dana. Ps. bouvieri A. M.-Edw. 

 has a stridulating apparatus in which vibrations are produced by a ridge 

 on the 5th segment of the chelipeds, playing over the striated antero-lateral 

 margins of the carapace. Melia Latr. M. tessellata, frequents coral and 

 has the remarkable habit of carrying a live sea-anemone in the chela.* 



Fam. 4. Portunidae. Carapace depressed, usually widest at the last 

 antero-lateral spine. 5-9 teeth on the antero-lateral margin ; the 5th legs 

 of the trunk usually flattened and adapted for swimming. Carcinus Leach. 

 7th segment of 5th legs narrowly lanceolate, antero-lateral margins of 

 shell 5-toothed. C. moenas (Perm.) the common shore crab of the British 

 Islands. Pcrtunus, Fabr. Frontal border 5-toothed ; last two segments of 

 5th legs flattened, the last joint ovate. P. puber (L.) the velvet crab, 

 P. depurator (L.) and 6 other spp. are British. Portumnus Leach, 7th 

 segment of 5th legs lanceolate. P. variegatus Leach, British. Platyonichus 

 Latr. 7th segment of 5th legs broadly oval, good swimmers, as are spp. of 

 Polybius Leach. Scylla de Haan, carapace very broad, with 9 or more 

 teeth on the antero-lateral margin, and Charybdis de Haan, 7 or fewer 

 teeth on the antero-lateral margin, are brilliantly coloured ; Bathynectes 

 Stimpson, B. superbus (Costa) N. Atlantic (including Mediterranean) ; 

 B. longipes Risso, also British. 



Fam. 5. Podophthalmidae. Carapace widest anteriorly, front narrow 

 and spatuliform ; with greatly elongated eye-stalks. Podophthalmus Lam. 

 Euphylax Stimpson. 



Fam. 6. Cyclidae. Carapace orbiculate. Acanthocyclus, M. Edw. and 

 Lucas, A. Gayi M. Edw. and Lucas. Chili and Patagonia. 



* Cf. Borradaile. Gardiner's Fauna and Geography of the Maldive 

 and Laccadioe Archipelagoes, vol. i, p. 249. 



