MOLLUSC A. 



23 



with thin hut muscular parietes. The third stomach rf, is mem- 

 branous, and precisely resembles the plicated stomach of rumi- 

 imnts, in being disposed in large but delicate folds, by means of 

 which the alimentary matter contained in it is moulded into long 

 whitish cords. The fourth stomach e, is membranous, like the 

 crop, but smaller. It is remarkable that the gizzard contains a 

 narrow groove, running through its whole length, leading from 

 the first to the fourth stomach, and probably subservient to a 

 species of rumination. 



F. 44. Another view of the animal ; g, its protracted fora- 

 men; h h, the lower lamina, or border of the sustentaculum ; 

 t, the upper lamina, under the middle of which the shell is con- 

 cealed; k, a plumose feeler; /, the teutacula, at the base of 

 which the eyes are placed. 



FAMILY VI. PHYLLIDIACEA. 



The branchiae are situate under the margin of the mantle, 

 aud disposed in a longitudinal series around the body. The 

 animals all respire in water. 



Patella vulgata. PI. 60. f. 21. The body is entirely covered 

 by a shell ; the head provided with two pointed tentacula, and 

 the eyes situate at their exterior base ; the branchiae are dis- 

 posed round the body, under the margin of the mantle ; the 

 anal opening and generative organ on the right anterior side ; 

 shell univalve, concave, conical, and simple, without a spire. 



F. 23. The alimentary canal, a, the mouth ; b, the buccal 

 mass ; c, the tongue ; rf, the stomach ; e e, the intestine. F. 24 

 represents the tongue of the patella of its natural size ; f. 25. is 

 a portion magnified ; f. 26, 27, and 28, are the cartilaginous jaws. 

 This tongue is a narrow riband-shaped body, near three inches 

 long, of almost equal breadth throughout, except at the apex, 

 where it is soft and somewhat dilated ; the surface roughened 

 with three rows of teeth, the side rows alternating with the 

 middle one, which is quadritid, while the side teeth are divided 

 only into two points. There are also placed along each side a 

 double row of cylindrical tubes, whose apertures look towards 

 the base. This curious spinigerous tongue is never protruded 

 beyond the margin of the lips. It seems to be used for rasping 

 down the food ; and, in proportion as the anterior prickles are 

 worn away in this operation, and absorbed, another portion of 

 the tongue is brought forward to supply its place : but that 

 there may be no deficiency in its length, we find the apex soft 

 and vascular, where in fact a continual growth and additions 

 are going on. 



Chiton cinereut. PI. 60. f. 78. The head anterior, sessile 

 with the mouth below ; destitute of tentacula or eyes ; branchiae 

 disposed around the body, under the margin of the skin ; anal 

 opening at the posterior extremity. F. 93. The animal ex- 

 tracted, a a, the ventre ; c c c, the intestinal canal ; e, the 

 anal opening ; d d d d, the liver ; /, the ovarium. 



FAMILY VII. TRITONIACEA. 



The branchiae are placed exteriorly, and situated above the 

 mantle on the sides or oil the back. The animals respire in 

 water. 



The animals of this family are distinguished from those of 

 the other Gasteropoda, by the situation of their branchiae, which 

 are all exterior ; in several genera these appear to be a degen- 

 eration of the mantle, or to be formed by portions of it 

 having become branchial ; the body is always destitute of a 

 shelly covering, and neither have they one internally. All the 

 animals inhabit the sea. 



Doris argui. PI. 32. f. 9. The body oblong, plain, convex, 

 or subprismatic, bordered all around by a membrane extend- 

 ing to each side of the head ; mouth placed anteriorly and 

 below; four tentacula, two of which are situate in a hollow 

 on the body, and the two others near the mouth ; anal opening 

 near the base of the back, surrounded by projecting, lacineated 

 and fringed branchiae ; generative aperture on the right side. 

 See Conchology, Vol. II. p. 378. 



Tethyt leporina. PI. 60. f. 30. The alimentary canal, a, 

 the proboscis ; b, the oesophagus ; c, the stomach ; d, the Intes- 

 tine ; e, the hepatic duct; /, the liver ; g, the hepatic artery ; 

 A h, salivary glands the parts are laid open. 



F. 29. The horny jpws of a Tritonia. 



ORDER V. PTEROPODA. 



Destitute of any shell, foot, or arms, either for locomotion or 

 seizing their prey ; but provided with two opposite and simi- 

 lar fins, fitted for swimming. 



The animals of this order are provided with two opposite 

 fins ; they are mostly of a small size, and either destitute of ap- 

 pendages, or having very short ones, situate at the head ; 

 some species are provided with a thin cartilaginous or horny 

 hell. 



Hyaltea tridentata. PI. 60. f. 36. Body enveloped in a shell, 



with two opposite retractile fins inserted at the sides of the i " =- " > "i"; ""<" 

 mouth; head indistinct ; mouth terminal at the junctions of | adductor muscle of the oyster, 

 the fin ; destitute of eyes ; branchiae lateral. 



CLASS II. 



ACEPHALOUS MOLLUSCA, 



OR SOFT ANIMALS DESTITUTE OF A HEAD. 



The second great division of testaceous Mollusca. consists of 

 mi mala which are destitute of any apparent head, and have 

 been denominated by Lamarck, CONCHIFEHA. Their mouth is 

 concealed in the bottom, or between the folds of their mantle, 

 which is usually doubled and incloses the body, in the same 

 nanner as a book is clasped over by its' cover ; but it often 

 lappens, that, in consequence of the two lobes uniting before, 

 t forms a tube ; sometimes it is closed at one end, aud then it 

 represents a sac. The mantle is generally covered by a calcari- 

 ous, testaceous bivalve shell united by a hinge or ligament, and 

 In some instances the shell is multivalve; in two genera, how- 

 sver, it is only of a cartilaginous or membranaceous nature. 

 The animal is always attached to this shelly covering by 

 strong muscles, by means of which it can open or close the 

 sides of its covering at pleasure. The brain is situated over 

 the mouth, where one or two other ganglia are observable. 

 The branchiae or gills, generally consist of large lamellae cov- 

 ered with vascular meshes, under or between which passes the 

 water; and are more simple in those genera which are desti- 

 tute of a shell. The leaflets of which the branchiae are com- 

 posed are generally crescent-shaped, placed on each side of the 

 cloak, covering the abdomen of the animal upon the sides of 

 which they are attached in pairs; they are formed of a tissue 

 of small vessels arranged close together, like the pipes of an 

 organ. From these branchiae the blood proceeds to the heart, 

 which is placed towards the back, is very small, but provided 

 with venous and arterial vessels. The liver is extensive, and 

 embraces the stomach and the greater proportion of the alimen- 

 tary canal. 



The mouth is always devoid of teeth, and is capable of only 

 receiving the molecules, conducted to it by the water ; at each 

 side of the mouth are four thin triangular leaflets, which are 

 the extremities of the lips. Some species are provided with 

 two stomachs. 



The whole animals of this division fecundate themselves, and 

 in many of the species, the young ones are extremely numer- 

 ous, and pass some time in the thickness of the branchiae before 

 quitting the parent. The whole acephala are aquatic ani- 

 mals. 



The foot of the animal when it exists is a mere fleshy mass, 

 the motions of which are effected hy a mechanism analogous to 

 that which acts on the tongue of the mammalia. 



The Conchifera of Lamarck are separated into two orders as 

 follows : 



ORDER I. MONOMYARIA. 



With but one internal muscle of attachment, and the shell 

 marked interiorly with one subcentral muscular impression. 



SECTION I. 



Ligament none, or at least unknown, or replaced by a ten- 

 dinous cord, which supports the shell. 



FAMILY I. BRACHIOPODA. 



With two opposite ciliated arms, placed near the mouth, 

 rolled up in a spiral form when the animal is in a state of repose; 

 mantle provided with two separate lobes before, which envelop 

 the body. Shell bivalve, adhering directly, or by means of 

 a tendinous cord to marine substances. 



Lingula anatina. PI. 18. f. 1. The shell is elevated on a 

 fleshy tendinous peduncle aud fixed to marine bodies. 



FAMILY II. RUDISTA. 



Nothing is known of the animal, nor of the ligament and 

 hinge of the shell; the valves are very unequal ; and no distinct 

 hooks are visible. 



Crania personata. PI. 60. f. 75. 



SECTION II. 



Ligament not marginal, but inclosed in a hollow space nnder 

 the beak, always perceptible, and never forming a tendinous 

 cord under the shell. 



FAMILY I. OSTRACBA. 



Ligament -interior, or at least partly so; shell irregular, 

 foliaceous, and sometimes papyraceous. The animal has neither 

 foot, arm, nor projecting siphon. 



Anomia epltippittm. PI. 60, f. 41. 



Ostrea Edulii, the Edible oyster, pi. 60, f 73. The animals 

 of this genus, of all others, appear to possess faculties, 

 the lowest in the scale of animal existence. Many are fixed to 

 rocks, or other bodies under water, and therefore are incapable 

 of seeking food, and are entirely dependent upon such as is 



rried to them by the motion of the water. F. 98 shows the 



