24 



MOLLUSTA. 



FAMILY II. I'KCTBNIDEf. 



Ligament either interior, or partly so, being discoverable in 

 tome i through an opening in the joint; shell in general regular, 

 compart, and not folirweous. Some genera fix themselves to 

 marine bodies, by a by.-sns, while in others the lower valve is 

 immovably attached ; and many of the pectens are at liberty. 



Spondyltu gaderopu*. PI. CO. f. 52. 



Pecten Jacobaut. PI. CO, f. 77. The animals of this genus 

 possess considerable powers of locomotion, which was well 

 Known at the time Aristotle wrote. They have the power of 

 removing themselves from one place to another, on dry land, by 

 successive leaps. This has been fully established by recent ex- 

 periments. A basket filled with the Pecten opercularit, or 

 common edible scallop, has been placed on the sea shore, near 

 the edire ot tne water, when all the individuals have speedily 

 found their way to the sea. They have but a small oval foot 

 placed on a cylindrical pedicle, between a sac-like abdomen 

 that is suspended between the branchiae. Some species swim 

 with rapidity by suddenly opening and closing their valves. 

 The mantle is surrounded by two ranges of filaments, several 

 of the external ones being terminated by a little greenish glo- 

 bule. The mouth has numerous branched tentacula instead of 

 the four usual labial leaflets. 



Lima tquamuta. PI. 60. f. 72. The mantle is provided with 

 numerous filaments of different lengths, but destitute of tuber- 

 cles, and more internally, with a large border which closes the 

 opening of the shell, and even forms a veil in front. The foot 

 is small, and the hyssus minute. The lim;r swim with great 

 rapidity, by opening and closing their valves. 



SECTION III. 

 Ligament marginal and elongated. 



FAMILY I. MALLBACEA. 



Ligament marginal, sublinear, and either simple or inter- 

 rupti d by crenulatious ; shell foliaceous or more or less in- 

 equivlve. 



Avicula Tarentina. PI. 60. f. 90. abed, the mantle, the 

 duplicate of which contains the ovariuu, ffg g ; the byssus, 

 ii i ; the abdomen, k ; s, the anal opening. 



FAMILY II. MYTILACEA. 



Hinge with a sub-interior ligament, which is marginal, 

 linear, and very entire, occupying a great part of the anterior 

 border ; shell but seldom foliaceous. Nearly the whole of this 

 family attach themselves to marine bodies by a byssus. They 

 have a tongue-shaped foot, by the aid of which they attach 

 their byssus to extraneous substances. 



Pinna nobilis. PI. 60. f. 91. a, b, c, d, lobes of the mantle ; 

 gg, hh, adductor muscles ; xf, part of the abdomen. The ani- 

 mal is elongated like its shell; it is destitute of projecting 

 siphons, and has a conical foot ; the mantle is close along the 

 side of the ligament ; the foot resembles a small tongue ex- 

 cavated by a sulcus, and is provided with a small transverse 

 muscle situated at the acute angle formed by the valves, near 

 which is the mouth. By the side of the vent, which is behind 

 this large muscle, is a conical appendage, peculiar to the genus, 

 susceptible of expansion and elongation, the use of which is un- 

 known. 



Mytilu* edulit. PI. 60. f. 11. F. 76 shows the animal. 



FAMILY III TRIDACMTES. 



The shell is transversely eqnivalve, with the muscular im- 

 pressions situated under the middle of the upper margin, and 

 prolonged on each side ; the mantle is close and perforated 

 by three holes, through one of which passes the foot; the 

 second furnishes an entrance and exit for the water requisite 

 for respiration ; and the third is a passage for the excretions ; 

 the two latter not being prolonged into tubes as in the Mytil- 

 acea. 



Tridacnn gigas. PI. CO. f. T7. The animal is very singu- 

 lar, and unlike most others of this class, being pressed out of 

 the shell in front instead of being placed within the valves. 

 The anterior side ot the mantle is widely opened for the pas- 

 sage of the byssus ; a little below the anterior angle is another 

 opening which transmits water to the branchiae, and in the 

 middle of the inferior side is a third and smaller one which cor- 

 responds to the vent, so that the posterior angle transmits 

 nothing and is only occupied by a cavity of the mantle open at 

 the third orifice. There is but a single transverse muscle cor- 

 responding to the middle of the valves. 



The tendinous byssus by which these gigantic shells some- 

 times weighing 300 pounds attach themselves to rocks, is so 

 thick and strong that an ax is required to sever it. Nearly 

 allied to this species is Tridama iquamota, pi. 18. f. 27. 



ORDER II. DIMYAIRA. 



Shell having two distinct and lateral muscular Impressions, 

 which are deep and widoly separated, being placed near the 

 lateral extremities of the valves. 



SECTION I. 



Shell always inoquivnlve and irregular. 



FAMILY I. CHAMACEA. 



Shell inequivalve, irregular, and adherent ; with two separate 

 muscular impre*>ions; ligament placed externally; the animal 

 provided with short, separate siphons. 



Chama gryphoidet. PI. 60. f. 54. 



C/iamii antiquata. PI. 60. f. 5ft. ab, the lohes of the man- 

 tle ; c, the abdomen ; dd, the foot. 



SECTION 11. LAMELLIPEDES. 



FAMILY I. NAYADF.S. 



This family consists of fresh water shells ; the hinge some- 

 times provided with an irregular, simple, or cleft tooth, and a 

 longitudinal prolonged one; sometimes destitute of any ; or is 

 furnished in its whole length with irregular granular tuber- 

 cles; the posterior muscular impression compound; and the 

 lunlicines often decorticated ; the muscular impressions are la- 

 teral and distant, that of the posterior side being composed of 

 two or three distinct, unequal impressions ; the animal is des- 

 titute of any projecting tube or siphon ; the foot is elongated, 

 transverse, and rounded, which it protrudes between the 

 valves, and uses to change its position. 



Anadonta cygnfa. PI. 60. f. 43. a, the mouth, into which 

 a bristle has been introduced ; b, the stomach, un<ier which the 

 intestine makes five turns in the foot amidst the ovary, and 

 then as it returns, runs posteriorly along the back of the animal 

 beneath the hinge, and above the respiratory organs, passing 

 through the midst of the heart, c, and opening at d above the 

 posterior muscle closing the shells, beneath the small tube of 

 the cloak. This description applies generally to most trivalves, 

 but in the oyster the rectum does not pass through the heart. 



Unio pictorum. PI. 60. f. 49. The animal has two tubiform 

 openings formed of the posterior extremity of the mantle, and 

 furnished with numerous and small tentacula; it has no bys- 

 sus; foot large, rounded and muscular; it is hermaphrodite 

 and produces its young alive. Lives in mud, at the bottom of 

 lakes and rivers. 



FAMILY II. TRIGONACEA. 



Primary teeth of the shell lamelliform, and striated Iraos- 

 versely; ligament exterior. 



Caitalia ambigita. PI. 18. f. 35. 



FAMILY III. ARCACEA. 



Primary teeth of the shell small, numerous, and disposed in a 

 line on each valve of the shell, either in a straight or inter- 

 rupted series. The valves do not close perfectly in the centre, 

 in consequence of having a horny plate or fillet placed before 

 the abdomen of the animal, that serves as a foot, and by which 

 it adheres to submerged bodies. 



Area Note. PI. 60. f. 59. 



Area barbata. PI. 60. f. 70. a, the foot. 



Pectunculus Pilosus. PI. 60. f. 56. F. 74, animal of do. 



FAMILY IV. CARDIACEA. 



Primary teeth of the shell irregular, both in their form and 

 situation, and having generally one or two lateral teeth. In 

 the animal, the mantle is open before, and there are besides, 

 two separate apertures, one for respiration and the other for 

 the fceees, which are prolonged in tubes, sometimes distinct, 

 and at others united in one single mass. There is always a 

 transverse muscle at each extremity, and a foot generally used 

 for locomotion. Those which are provided with long tubes 

 always live in ooze or sand. 



Itocardia cor. PI. 60. f. 98. In all the species the lig- 

 ament of the shell is exterior, and very short ; two distinct 

 muscular impressions. The animal is furnished on each side 

 with two unequal tubes, ciliated at their orifices, and on the 

 other side with a large muscular foot. 



Cardium rusticum. PI. 60. f. 60. ae, the tracheae ; a, part 

 of the abdomen ; bb, the branchiae ; c, the adductor muscle. 



FAMILY V. CONCHACEA. 



Shell with three primary teeth, at least in one valve, and the 

 other with a similar number, or less in some species ; sometimes 

 provided with lateral teeth. The animal has generally two 

 tubes or siphons projecting from its mantle, one of which an- 

 swers the purpose of a passage for the water to the branchiae, 

 and the other for dejected matters; the foot is lamelliform. 

 All the animals of this family inhabit sand or mud. 



Subdivision I. 



Generally destitute of lateral teeth ; inhabiting the ocean; 

 siphons of the animal elongated and unequal ; the foot broad 

 and projecting. 



Venut Verrucota. PI. 60. f. 39. 

 Chythetea Cfiiojte. PI. 60. f. 48. 

 i Artemii orbiculata. PI. 60. f. 53. 



