DECAPODA. 



413 



Tliefirst section, PiNNiPEDES, have the liind pair of legs terminated by a flattened plate for s-u'imming, 

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



Anioii£;st these swimming or shuttle-crabs, as they are termed, are especially to be noticed the exotic species, 

 composin]2;the genus Matiita, 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 swinmiing. Tlie same is also the case, 

 but less strongly, in Leach's genus Pohjbius, coTisisting of the single species, P. Hen^Ioidi, found on the Dcvon- 

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

 ming, the genus Orithyia, Fabr., consisting of a single Cliincse 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 Podopfhalmus, 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 form, compose the genus 

 Portiinun, Fab., amongst which may be mentioned Cancer pit'.er, Linn., and Cancer Mienas, Linn. {Carcinns 

 Ma-)im, 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 tlie carapax arched in front and nan*owed 

 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 arc folded backwards. 



C(uici.'r^f(i(/i'rii.':, Linn., the common large edible crab, lias the carapax very ijroad, 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 tisherman may twice a day take 

 with little work a vast number of specimens, after hai'- 

 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. (Lnt. Conipend.p. 80.) Mr. 

 Bell has described some beautiful exotic species of this 

 genus in the Transactions of the Zoological Society, 

 vol i 1 The frenus Xantho, Leach, is nearly allied to the 



lalc, ff; and oJ ■ •J " , . , ■ ■. . i 



preceding, but havmg the external antenna short, and 

 The typical species, X fforida, Leach, inhabits our coasts. 



The -enus Perlmela, Leach, has a longer carapax, with the edges" strongly toothed, the eight hind le-s equally 

 compressed, and longer antenna. P. denticulata. Leach, occurs in various parts of ou)- coast, and m the Medi- 

 tcrranean. . 



The -enus AfeJecyrlas, Leach, has tbe carapax nearly rounded, and dentated at the smes, the tail narrower than 

 in the' preceding; the lateral antenna elongated, the claws very strong, and rather short. The t>Te of this 

 -em.s is the Cancer l-denlaim oi Montague, bv whom it was discovered ou the coast of Devonshire. Other 

 -enera, which it would occnpv too much space to notice, have been separated by Leach, Latredle, ana otliers. 

 Arnon^'-st them, however, the two exotic genera, Mursea, Leach, and Ilepatus, Lat., are distinguished by their 

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

 named CristiTuani, or crested-handed Crabs. 



iij. 2. — O'ncr PagiiTUS, Linn,, 

 [he fc'male, b. 



nserted in the external canthus of the eye. 



l\Ir. M'Leny's nrrangemeiit of tlic Bradiyui 

 part of Oie Illustrations of tlie Ziioliif^y of Sou 

 lislifd, is as follows ; — 



Tribe Tetrni^onostoma. Aiinloiries. 



PUHiotherinn[Parasit. Crabs) SlicU urbicuinr 

 Gnpsina (Squure Crabs) 



Shell quartrilater-a 



Caiierina [Arched Crabs) 

 Parti cnopina (Rucky Cra 

 Inachira (Triangular Crabs) 



( Shell nruuateii.ivith ihei , 

 tory J 



"> 1. r„,„„,.„ 



feet often n: 

 r Shell uneven, 

 \ crested feet j" 



j- Shell subtriangiiW,rind> 

 I generallj' spiiicd i 



