MOLLUSCOUS ANIMALS. 



581 



fire fluviatilc, the animals respiring in water. Paludina 

 iinpura, pi. 24, f. 1 1. Valvata piscinalis, pi. 24. f. 61. 



FAMILY vm. MELANIDES. 



The margins of the aperture disunited, and the right 

 one edged; animal provided with two tentacula. Pi- 

 rena Madagascar -crisis, pi. 31, f. G7. 



FAMILY ix. LYMN/ECEA. 



With an oblong acutely tapering spire, generally 

 smooth on the external surface, and having the outer 

 margin of the aperture always acutely edged, and not 

 reflected. Animal amphibious, generally destitute of 

 an operculum, and the tentacula flattened. Lymnaea, 

 staynalis, pi. 24, f. 4. 



FAMILY x. COLIMACEA. 



Shells acutely spiral, with no projecting parts on their 

 exterior, except the markings of their periodical addi- 

 tions; the right margin of the aperture frequently re- 

 flected outwards; the tentacula are cylindrical, and 

 usually four in number, but two in others, and destitute 

 of operculum. They are terrestrial animals. Cydostoma 

 dcrjans, pi. 24, f. 10, Succinea amphibia, pi. 24, f. 58. 

 Pupa seocdentatus, pi. 24, f . 57. Helix aspersa, pi. 24. f . ] 5 ; 

 f . 92, apparatus of vision in Helix Pomatea ; f. b'5, toothed 

 cartilage of do. 



ORDER IV. GASTEROPODA. 



Body never spiral, destitute of any shell, provided with 

 a muscular foot attached its whole length under the 

 belly, for the purpose of locomotion. Some of the animals 

 of this division are naked and destitute of any calcareous 

 covering, others are provided with a dorsal plate, and a 

 third series have a shell which is more or less concealed 

 in their mantle. The animals of this order are limited 

 by Lamarck to those whose bodies are straight, and 

 never spirally convoluted, and which are provided with 

 a muscular disk or foot, united to the body nearly its 

 whole length. F. 66, pi . 24, exhibits the nervous system 

 of the Aplysia; f. 67,* Clio Borealis; f. 67 , the same in 

 the act of swimming. 



SECTION I. PNEUMOBRANCHI^. 



Branchiae in the form of a vascular net on the wall of 

 a, particular cavity, opening by a hole, which the animal 

 contracts and dilates at pleasure. 



FAMILY i. LIMACINJE. 



Branchiae in the form of a vascular net on the parti- 

 tion of a particular cavity, the aperture of which the 

 animal can contract or dilate at pleasure. The body of 

 the animals is elongated, and they crawl by means of a 

 ventral disk bordered on the sides by a very narrow 

 mantle. Vitrina bcryllina, pi. 24, f. 7. Testacella Seutu- 

 lum, pi. 24, f. 6. Limax ater, pi. 27, f. 25. Onhidium 

 Typha, pi. 27, f. 7. 



SECTION II. HYDROBRANCHL3L 

 FAMILY in. LAPHYSIACEA. 



The branchiae are situated in a particular cavity to- 

 wards the posterior part of the back, and covered by an 

 opercular scutellum; they are provided with tentacula. 

 The animals of this family resemble large snaile, but 

 have a thicker body, and are broader towards the pos- 

 terior part, and have a larger margin to their mantle; 

 the head projects, and is provided with four tentacula, 

 two of which are placed near the mouth, and the other 

 two more behind. The branchial scutellum is corneous 

 or cretaceous. Dolabella callosa, pi. 31, f. 88. LapJiysia 

 deplians, pi. 27, f. 8, pi. 24. f. 17. 



FAMILY in. BULLACEA. 



Head very distinct: the branchiae are situate in a 

 particular cavity, towards the posterior region of the 

 back, and covered by a mantle; they are destitute of 

 tentacula, and branchial operculum. Some species are 

 unprovided with either exterior or interior shell, and 

 in others the shell is completely concealed in the man- 

 tig, and there are several which have an external shell 



attached by a muscle. Bulla liydatis, pi. 24, f. 86. 

 This figure exhibits the back of the shell, with the 

 lateral iin-like membranes protruded a. F. 87. The 

 gizzard magnified, a, a, a, the tips of the plates cover- 

 ed by a thin membrane, and surrounding a muscular 

 integument, thickened at the upper part b; the part 

 attached to the mouth c, with the oesophagus communi- 

 cating with the gizzard; rf,the intestinal canal. F. 88. 

 The gizzard laid open at its anterior end, showing the 

 three corrugated corneous plates e, e, e, with then- con- 

 necting ligaments/", magnified. Bulla aperta, pi. 24, f. 83 

 and 68. Lateral lobes of the foot thickened and reflect- 

 ed upwards; head indistinct; destitute of tentacula; 

 branchiae dorsal ; shell concealed in the mantle, a. F. 

 84, the gizzard composed of three testaceous plates, 

 showing the smaller plate b, with the connecting liga- 

 ment c. F. 85, another view of the gizzard, showing 

 the two larger plates d d, with their connecting liga- 

 ments; e, the gullet,/, the alimentary canal. 

 FAMILY iv. CALYPTRACEA. 



The branchiae are situate in a cavity on the back ncrii 

 the neck, and projecting beyond or included in the ca- 

 vity ; shell always placed exteriorly Ancylusfluviatilis, 

 pi. 24, f. 9. 



FAMILY v. SEMIPHYLLIDIACEA. 



The branchiae are situated under the margin of the 

 mantle, and disposed in a longitudinal series on the 

 right side of the body ; respiring in water. Pleurobran- 

 clius phtmula, pi. 24, f. 14, f. 22. Alimentary canal; a 

 the first stomach; c the second stomach; d the third 

 stomach ; e the fourth stomach. The oesophagus dilates 

 into a membranous crop a ; at the lower part of which, 

 b, the bile is poured in. It communicates by a narrow 

 cardia with the second stomach c, which is a gizzard 

 with thin but muscular parietes. The third stomach 

 d, is membranous, and precisely resembles the plicated 

 stomach of ruminants, in being disposed in large but 

 delicate folds, by means of which the alimentary mat- 

 ter 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 pro- 

 bably subservient to a species of rumination. F. 44. 

 Another view of the animal; g, its protracted foramen; 

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

 z, the upper lamina, under the middle of which the shell 

 is concealed; k, a plumose feeler; I, the tentacula, at 

 the base of which the eyes are placed. 



FAMILY VI. PHYLLIDIACEA. 



The branchiae are situate under the margin of the 

 mantle, and disposed in a longitudinal series around 

 the body. The animals all respire in water. Patella 

 vulgata,p\. 24, f. 21. F. 23. The alimentary canal, a, 

 the mouth; 6, the buccal mass; c, the tongue; d, the 

 stomach ; e e, the intestine. F. 24, represents the tongue 

 of the patella of its natural size; f. 25, is a portion mag- 

 nified; f. 26, 27, and 28, are the cartilaginous jaws. 

 Chiton cinereus, pi. 24, f. 78. F. 93. The animal extracted. 

 a a, the ventre; ccc, the intestinal canal; e, the anal 

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



FAMILY VII. TRITONIACEA. 



The branchiae are placed exteriorly, and situated 

 above the mantle on the sides or on 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 exter- 

 ior; in several genera these appear to be a degeneration 

 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 argus, pi. 27, f. 

 9. Tethys leporina, pi. 24, f. 30. The alimentary canal, 

 a, the proboscis; b, the oesophagus; c, the stomach; rf, 

 the intestine; e, the hepatic duct; f, the liver; fl, the 

 hepatic artery; h h, salivary glands the parts arc laid 

 open; f. 29. the horny jaws of a Tritonia. 



