ARTICULATA. 117 



In the Brachyura {pi. 7S,figs. 1-9), the carapace is generally transverse, 

 and square, oval, or circular, the abdomen is small, without a caudal fin, it 

 is bent beneath and received into a depression of the thorax, and is not used 

 in locomotion. The eye peduncles are generally longer than in the Macrura ; 

 there are two pairs of antenna3, one pair of mandibles, two of jaws or 

 maxillffi, three of foot-jaws, succeeded by ten feet, the first pair having a 

 pinching claw, the rest simple, and adapted in most cases for walking, but 

 sometimes for swimming. The abdomen is wider in the female than in the 

 male, and is composed of seven segments ; but some of these are sometimes 

 united together in the female, so as to present from four to six. Linnaeus 

 included the various genera of Brachyura in his genus Ccmcer, which 

 corresponds very nearly to the English name crab. They are divisible into 

 four families. 



2^am. 1. Zeucodadce. This family, called Oxystomes by Milne Edwards, 

 includes the four sub-families, Cala])iyina\ Leucosiime, Corystiina;^ and 

 DorippiinoB., in which the shell is more or less orbicular, the eyes generally 

 small, and the external foot-jaws triangular. 



The Calapjnnce form part of Latreille's Cryptopodes., named from the 

 feet being partly hidden by the projecting margin of the carapace. The 

 ZeucosimcB are much like the Cancridse or ordinary crabs. Philyra [pi. 

 Y8, fig. 7) is a genus of small Crustacea, with the carapace circular and 

 depressed. In the Corystiince.^ the external antenna?, are robust and rather 

 long, and the sternal plate narrow. In Corystes, the anterior feet are much 

 larger in the male than in the female, and the abdomen has five articulations 

 in the former and seven in the latter. The Dorippiinco {Doi'ippe.^ pi. 78, 

 fig. 8), which form part of Latreille's N'otopodes, have the sternal plate 

 circular and bent upwards posteriorly, the cheliforni feet short, the two next 

 pairs long, and the one or two last pairs, which are generally much reduced 

 in size, are placed higher than the others, as if upon the posterior part of 

 the back. 



Fam. 2. OcijpodidcE. This family of Leacli corresponds to the Catame- 

 topes of Milne Edwards, in which the carapace is depressed, rhomboidal or 

 ovoid, and the eye peduncles long and slender. The following are the sub- 

 families : Thelphitsinoe^ Gecardninm.^ Pi7inotherinoB^ Ocypodinm^ Gonopla- 

 cincB, and GrapsincB. 



Thelphusa is a genus of crabs which lives along the banks of freshwater 

 streams. The Gecardninm {GeGardnus.pl. 1^^ fig. ^) are remarkable for 

 having branchife adapted to aerial respiration. They live among damp forests 

 in holes which they make, and where they moult. Their food is vegetable, and 

 they generally move about at night, or in wet weather. They visit the sea at 

 certain periods, for the supposed purpose of depositing their eggs. They run 

 with great agility, and like the crabs in general, in either direction. Pinnotheres 

 ostreum is commonly found wnthin the shell of Ostrea virgimana of the 

 United States coast. In this genus the males are much smaller and more 

 rare than the females. They are found within the shell of various bivalve 

 Mollusca, as Pinna and Mytilus, where they are compensated for the 

 weakness of their shell. The OcypodincB {Ocypoda., pi. 78, fig. 6 / Gela- 



ICON'- ' "*'""i ENCVCLOP^DIA. VOL.11. 21 321 



