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. Henslowii, 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 Orithyia, 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 form, compose the genus 
Portunus, Fab., amongst which may be mentioned Cancer puber, Linn., and Cancer Moenas, Linn. {Carcimis 
Moenas, 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 joint 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 
inserted in the external canthus of the eye. The typical species, X.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 antennae. P. denticulata, Leach, occurs in various parts of our coast, and in 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 antennae elongated, the claws very strong, and rather short. The 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, Mur sea, 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 Brachyura, as given in the 3rd 
part of the Illustrations of the Zoology of Southern Africa, just pub- 
lished, is as follows ; — 
Tribe Tetragonostoma. Analogies. Tribe Trigonostoma. 
Pinnotherina(Parasit. Crabs) Shell orbicular Dromiina. 
Grapsina (Square Crabs) Shell quadrilateral Dorippina. 
j Caucrina (Arched Crabs) 
Parthenopina (Rocky Crabs) 
Inachina (Triangular Crabs) 
. Shell areuated.mththei coystrina. 
I feet often natatory J 
{ Shell uneven, with 1 ^ , 
crested feet } 
{ Shell subtriangular,and 1 
generally spined / Leucosina.] 
