DECAPODA. 



413 



The first section, Pinnipedes, have the hind pair of legs terminated by a flattened plate for swimming, 

 and these species are accordingly met with at a distance from the coasts. 



Amongst these swimming or shuttle-crabs, as they are termed, are especially to be noticed the exotic species, 

 composing the genus Matuta, Fab., having the carapax nearly circular, and armed on each side with a strong spine, 

 and with the four posterior pairs of legs terminated by a dilated plate for swimming. The same is also the case, 

 but less strongly, in Leach's genus Polybius, consisting of the single species, P. Hensloicii, found on the Devon- 

 shire coast. Amongst the species with only the last pair of legs dilated at the extremity into a plate for swim- 

 ming, the genus Orithi/ia, Fabr., consisting of a single Chinese species, is distinguished by the tail of the males 

 being distinctly seven-jointed, whereas there are only five joints in the males of all the other Pinnipedes, the females 

 alone having seven joints. Amongst these the genus Podopthalmus, Lamarck, has the carapax transverse, and 

 armed at each side with a very long spine ; the ocular peduncles are very long (P. spinosus, Latr., Isle of France) ; 

 others which have the ocular peduncles short, and which are of the ordinary crab-like fonn, compose the genus 

 Portunus, Fab., amongst which may be mentioned Cancer pu'>er, Linn., and Cancer Moenas, Linn. (Carcinus 

 Mccnas, Leach), two small species, commonly used as articles of food by the lower orders in London. The last- 

 named species is exceedingly abundant ; the terminal jomt of the hind legs is much narrower than in the preced- 

 ing groups, and thus this species forms a passage to — 



The second section, Arcuata, in which the tarsus, or last joint of all the legs, is conical, and some- 

 times compressed, but never forming a swimming plate, and the carapax arched in front and narrowed 

 behind, with the claws of equal size in both sexes, and the tail is composed of the same number of 

 segments as in the Portuni. The true Crabs, composing the restricted genus Cancer, Fabr., are the 

 types of this section, and are distinguished by having the third joint of the outer foot-jaws emarginate 

 or sinuated near the inner extremity, and nearly square. The antennae scarcely extend beyond the 

 front, with but few joints, and are folded backwards. 



Cancer pagurus, Linn., the common large edible crab, has the carapax very broad, and arched for a great dis- 

 tance along the sides, each side having nine festoons, and the middle in front with three short teeth : the claws 



are large, and the fingers black and armed with obtuse 



points. It sometimes reaches nearly a foot in breadth, 

 and is of common occurrence on the coasts of England 

 and France. [It is captured by sinking pots, baskets, 

 or nets, baited with decaying animal matter, to a con- 

 siderable depth in the ocean, along the rocky coast. 

 During the summer months it is very abundant, especi- 

 ally where the water is deep ; and at low tide they are 

 found in holes of rocks in pairs, male and female, and if 

 the male be taken away another will be found in the 

 hole at the next recess of the tide. By knowing this 

 fact, an experienced fisherman may twice a day take 

 with little work a vast number of specimens, after hav- 

 ing discovered their haunts. In the winter they are 

 supposed to burrow in the sand, or to retire to the 

 deeper parts of the ocean. (Ent. Compend. p. 86.) Mr. 

 Bell has described some beautiful exotic species of this 

 genus in the Transactions of the Zoological Society, 

 vol. i.] The genus Xantho, Leach, is nearly allied to the 

 preceding, but having the external antennae short, and 



Fi|r. 2. — Cancer Pagiifrulf Linn., with the tail of tlie male 

 the female, b. 



inserted in the external canthus of the eye. The typical species. A', florida. Leach, inhabits our coasts. 



The genus Perimela, Leach, has a longer carapax, with the edges strongly toothed, the eight hind legs equally 

 compressed, and longer antenna;. P. denticitlata, Leach, occurs in various parts of our coast, and m the Medi- 

 terranean. 



The genus Atelecyclus, Leach, has the carapax nearly rounded, and dentated at the sides, the tail narrower than 

 in the preceding; the lateral antenna elongated, the claws very strong, and rather short. Tlie type of this 

 genus is the Cancer 1-dentatus of Montague, by whom it was discovered on the coast of Devonshire. Other 

 genera, which it would occupy too much space to notice, have been separated by Leach, Latreille, and others. 

 Amongst them, however, the two exotic genera, Mursea, Leach, and Hepatus, Lat., are distinguished by their 

 claws being greatly compressed, so that they have subsequently been separated by Latreille, as a section thence 

 named Cristimani, or crested-handed Crabs. 



Mr. M'Leay's arrangement of the Bratliyura, as given in the 3r<i 

 part of the Illustrations of the Zoology of Southern Africa, just pub- 

 lished, is as follows:— 



Tribe Tetragonostoma. Analogies. Tribe Trigonostoma. 



Piiinotherina(Parasit. Crabs) Shell orbicular Uromiiiia. 



Grapsina (Square Crabs) SheU quadrilateral Doripiiina. 



, , „ , , I Shell arcuatcd,\vith the l „ 



Caiicrina (Arched Crabs < , . ,. . , e Coystriua. 



'-*• ^ ^ feet often natatory J 



,« . ^ L ^ r Shell uneven, with 1 ^ , 



I'artl.cnopina (Rocky Crabs) | „es,ed f^^.^ ]■ Calapp.na. 



. „ , , f Shell subtrianguUr.andl . 



Inachina (Triangular Crabs) \ „„ „,i„,d / Leucosu.a.) 



