CRUSTACEA. 



551 



seated on peduncles, which are sometimes movable, 

 and at others fixed : they have a distinct heart, and 

 a regular circulating system : their organs of repro- 

 duction are placed either in the feet or tail. 



In those genera where the head is not separated 

 from the trunk, the shield or covering envelopes the 

 whole thorax. In other genera the liead is distinct 

 from the body, which is divided into seven segments, 

 to the lower sides of which the feet are attached ; 

 these for the most part have a tail, consisting of 

 many segments. The limbs vary from ten to four- 

 teen, each having six articulations. The two ante- 

 rior limbs, and sometimes even three on each side, 

 are provided with forceps ; at other times they are 

 terminated by simple hooks, and in many instances 

 by appendages which fit them for swimming. 



The branchias in crustaceous animals, unlike those 

 of fishes, are external, although frequently conceal- 

 ed, and placed at the sides of the feet limbs, or 

 under the tail ; they are, however, more frequently 

 at the sides of the feet ; and consist either of fila- 

 mentary tufts, or pyramidal laminae. 



The mouth has usually two mandibles, a labium, 

 or lip below, and from three to five pairs of jaws. 

 The first, or first three pairs of these have been 

 termed feet-jaws. These small leg-shaped appen- 

 dages are not fitted for locomotion, but, being situat- 

 ed near the mouth, assist in the operation of reeding. 



The nervous system consists of a ganglion or 

 brain, situated above and before the intestinal canal, 

 with a continuous elongated double chord, having 

 ganglions placed on the lower surface of the body, 

 extending, in some instances, its whole length ; 

 while in others, it consists of a central medullary 

 circle, with radiated elongations. 



Many of the crustaceous animals have an acute 

 faculty of sight ; a number of them also possess 

 the senses of smell and taste ; but from their shelly 

 envelope their sense of feeling must be very blunt : 

 while their touch must be very sensible, from the 

 number of tentacula possessed by many of them. 



Since the phrenological system of Gall and Spurz- 

 heim has become known, it has suggested to various 

 naturalists a more definite mode of investigating 

 specific distinctions. The celebrated French natur- 

 alist Desmarest, has most successfully availed him- 

 self of the developments of the principal organs, in 

 the upper surface of the shield in crustaceous ani- 

 mals, in ascertaining and describing fossil species. 

 The different parts thus indicated have been termed 

 regions ; such as the stomachal region, occupying that 

 portion of the shield immediately behind the eyes ; 

 behind which, and near the centre is the genital re- 

 gion ; still farther back is the cardial region ; on 

 each side of the stomachal region, is placed the an- 

 terior heptic one ; and extending on each side behind 

 the cardial and genital regions, to the posterior mar- 

 gin of the shield, is situate the branchial region. 



Crustaceous animals live in various situations, suit- 

 ed to their organization ; some inhabit considerable 

 depths of the ocean, others are found on rocky 

 shores, or in muddy shallows ; some, such as craw- 

 fish, inhabit rivers, under stones and banks, while the 

 land-crab, a tropical species, takes up its abode in 

 inland situations, making periodical journeys to the 

 coast in immense numbers, for the purpose of deposiU 

 ing its eggs. 



The facility with which these animals can detach 

 one of their limbs, which may be seized upon by an 

 enemy, is not the least striking part of their history. 

 And this amputated limb they have the faculty of 

 reproducing ; which, however, is always of a less 

 size than the others, until it has once or twice chang 

 ed its crust. 



Some of the Crustacea have the property of emit- 



ting light in the dark. A singular luminous appear- 

 ance was noticed in the sea by Sir Joseph Banks, 

 while on his passage between the island of Madeira 

 and Rio de Janeiro. On a bucket of water being drawn 

 up, he discovered in it innumerable prawn-like crus- 

 tacea, to which he gave the name cancer fulgens. 

 The light was found to be sent forth from every 

 part or the body. Other species have the same 

 property, but in some it is confined to the region 

 of the brain. 

 Lamarck divides the Crustacea into five orders. 



ORDER I DECAPODA. 



The head is not distinct from the trunk ; branchiae formed 

 like leaflets, close to the base of the four feet-jaws, and hidden 

 under the sides of the shell. 



SECTION I. BRACHYURA. 



Branchiae, seven on each side, moving on a common axis ; 

 post-abdomen, bent underneath ; generally received into a ca- 

 vity beneath the pro-abdomen ; without a fin at the termina- 

 tion. 



FAMILY I. QUADRILATERA. 



Thorax nearly square, frequently heart-shaped ; anterior 

 angles expanded ; posterior extremity transversely truncated ; 

 front protruded, more or less inclined ; none of the feet termi- 

 nated by a fin. 



The genera of this family are Octypoda, Gelasimus, Myctris, 

 Pinnotheres, Gecarcinus, Plagusia, Grapsus, Gonoplax, Thel- 

 phusa, and Eriphia. 



Thelphusa fluviatilis, pi. 30, fig. 1. With very short exterior 

 antennae, placed near tue ocular pedicles ; having approximate 

 jaw-feet, which cover the mouth ; forceps, large, and nearly 

 equal ; hands, granular and oval ; the third pair of feet the 

 longest ; shell, cordiform, smooth, and depressed ; posteriorly 

 truncated, having the form of an H impressed on the middle ; 

 eyes, lateral, seated on short, thick peduncles. 



FAMILY II ABCUATA. 



The shell anteriorly arched, to nearly the centre of the sides ; 

 posteriorly narrowed and truncated. 



The genera are, Pilumnus, Cancer, Pirimela, Atelecyclus, 

 Podophthalmus, Lupa, Portunus, Tina, and 



Portunws corrugates, pi. 30, f. 2. Eyes, diameter of their pe- 

 duncles, with entire orbits ; anterior pair of legs equal, forcops 

 long; claws of the rest compressed, their base internally di- 

 lated ; fifth pair with depressed foliaceous claws ; transverse 

 and longitudinal diameters of the shell alike. 



FAMILY III. ORBICULATA. 



Orbicular, narrowed before, usually with two furrows ; ex- 

 terior feet-jaws with their third joint triangular. 



The genera are, Matuta, Orithyia, Corystes, Leucosia, and 

 Hepatus. 



Leucosia Urania, f]. 30, f. 3. Subrotund, very convex ; sides, 

 deeply canaliculated ; antennas, small, approximate, placed be. 

 tween the eyes, which are small; anterior pair of legs thickest, 

 provided with forceps. 



FAMILY IV. CBYPTOPODA. 



Nearly triangular ; vaulted, and dilated at the posterior an- 

 gles, for the feet in repose ; with large, crested, and compressed 

 forceps. 



The genera are, CEthra and 



Calapua tvberculata, pL 30, f. 4. Short, convex, posteriorly 

 broadest ; forceps, large, unequal, and compressed ; the other 

 feet short and simple : exterior antennae short, inner ones fold, 

 ed under the head ; third joint of the . set-jaws acute. 



FAMILY V. TRIGONA. 



Subovoid or triangular ; anterior extremity compressed and 

 pointed ; claws in the males frequently longer than in the fe- 

 males. 



The genera are, Parthenope, Eurynome, Pisa, Maia, Steno- 

 pus, Hyas, Inachus, Macropodia, Leptopodia, Pactolus, and 

 Lithodes. 



Pisa tetraodon, pi. 30, f. 6. Triangular, tuberculous, villous, 

 laterally and anteriorly dentated ; orbits having two slits be- 

 hind, and one below ; last five pairs of feet with dentated claws. 



FAMILY VI. NOTOPODA. 

 Having two or four posterior feet, inserted on. the back, or 



somewhat above the line of the rest. 

 The genera are, Hoinola, Ranina, Dromia, and 

 Dorippe, nodutosa, pi. 30, f. 6. Depressed, truncated , and 



spinous in front, sinuous behind ; surface, with elevations ; for. 



ceps, small, short, equal; the rest long, compressed; third 



pair longest, two last dorsal; exterior antennae setaceous; 



third joint of outer feet-jaws narrow, elongated, acute. 



SECTION II. MACROURA. 



Bodies longer than in former section ; post-abdomen carinated 

 above ; antennae terminated by filaments. 



FAMILY I. HIPPIDKS. 



Last abdominal segment lengthened, and foliaceous ; two an- 

 terior feet, tapering ; frequently with a monodactylous hand ; 



