444 CRUSTACEA. 



THE SECOND ORDER OE EXTOMOSTRACA — 



(T/ie Seventh and lusl af the Class Crustacea), — 



PCECILOrODA,— 



Is distinguished from the prcccdinf,'- hy the diversity in the form of the feet, of 

 which the anterior, of ;ii) indutermiiiatc numljcr, are ambulatory, or fitted for pre- 

 hension, and the otliers, lamelhform or pinnated, are branclrial, and iitted for swim- 

 ming. But it is especially in the absence of mandibles and maxilla; of the ordinary 

 form that they are separated from all the other Crustacea ; sometimes these organs 

 are replaced by the basal joint of the six anterior legs being armed with numerous 

 minute spines ; sometimes the organs of manducation consist cither in an external 

 siphon in the form of an inarticulated beak, or in some other instrument fit for 

 suction, but hidden, or very indistinct. 



The body is nearly always covered, either entirely or for the most pjart, by a 

 shell in the shape of a shield, composed of a single piece in the majority, but of 

 two parts in some, and always exhibiting two eyes at least when these organs are 

 distinct. Two of the antennae (Chellccra, Latr.) are in manj- in form of hooks, 

 and perform the functions as such. The number of their legs is twelve in the 

 greater number*, and of ten or twenty-two in nearly all the others. They reside 

 for the most part upon aquatic animals, and most commonlv on fishes. 



We divide this Order into two families, [Xyphosura and Sipuonostom.a,] which, m 

 my Families Natiirelles, comjioscd two separate orders. 



THE nUST FAIIILY OF IHECILOrOD.V,— 

 XvrnusuRA, — 

 Is distinguished from the followiug liy many cliaracters : they have no siphon ; the co.xre of the six paii'S 

 of fore-legs are lieset with minute teeth, aud perform tlie otEce of jaws ; tlie numlicr of legs is twenty- 

 two ; till- ten anterior, witli tlie exception of the two antriior in Ihe males, are tcriLiinated liy a tno- 

 fingercd claw, and inserted, as well as (lie two fnllowiiig, beneath a large scuiilunar shield; the latter 

 hear the oigans of generation, and are in the fiu'm of large leaves, as well as the ten fVdlowing, which 

 are hraneljial, and annexed to the under side of a second shield, which is terminated hy a very powerful, 

 horny, moveahle style, like a sword. These animals arc wanderers. They compose tlie genus 



Limidus, Fab., of which the species have received the name of [King Crabs], or crabs of the Moluccas. Tlie 

 nearly rounded body, somewhat elongated and narrowed behind, is divided into two parts, and covered by a solid 

 shell of two pieces, one for each division of the body ; it is very concave beneath, and exhibits 

 ' ' on Its upper side two longitudinal impressions, one on each side, and a central dorsal ridge. 

 The fore part of the shell, or tluit ^vhtch covers the front of the body, is nincll larger than the 

 other, and forms a large semdimar shield, having on its upper side two oval eyes, ivith very 

 numerous facets, in the form of minute grains, and situated one on each side on the outside of 

 the longitudinal ridge ; and at the anterior extremity of that of the centre, which e.xtenils tn the 

 pieces of the shell, are two small, simple eyes, close together. "Within the cavity of the anterior 

 Bhell is a small swollen labrum, ridged in the centre, terminated in a point, and above which 

 are inserted two small antenna;, in the form of small didaetyle claws, and elbowed in the middle 

 of their length, at the union of the tirst and foUowingjoint. Immediately beneath are inserted, 

 close together in pairs, in t-\vo lines, twelve legs, of which the ten anterior (the two (ir feiii' anf.'iior 

 in the males only excepted) are terminated by a didaetyle claw, and of which the tiasal joint is 

 advanced interiorly into a lobe armed with numerous minute spines, and performs the functions 

 of the inaxillai. These legs progressively increase in size, and, with the exception of the fifth 

 pair, are composed of six joints, including the moveable finger of the claw; the fifth pair have an additional 

 jiiint, anil also a curved appendage at the base, directed backwards, and composed of two joints; their fifth 



* Fourteen in some speci<.,s, QcLonJiii^r [o Leaclj ; l.ul the p.iir n lii,:!, fcriur .■mleii.tip. The Ari.'uli, m hkli, in respeet to tlieir locomotive 

 lie considers to be the anterior pair, u|ijicors to me to he the two in- 1 organs, are the tnosl |icrfecl, have only t»cl>e legs. 



