LIMX.EAD.B. 



LIMX.EAD.*. 



that UM animal carry their thclls in a direction opposite to that of 

 UM MtMnlity of turbinmUJ molluscs, and that the heart U placed in 

 th ff-nr*ff oo the right aide, and the respiratory orifice on the left, 

 xactiy UM reverse of their position iA most other*. But, he further 

 observes, the knowledge of UM animal U not indispensably necessary 

 to peon this a. the shell itaelf earrie* the demonstration, it being 

 only needful to obwrre on which aide of the obeli the very apex of 

 the wire U to be Men ; if we take that side for the upper, in con- 

 formity to the strict rule* of analogy, it will, he remarks, be evident 

 that the aperture U on the left-hand aide. Mr. Sowerby had for a 

 long time entertained great doubt about the identity of some of the 

 fowl specie*, which he U now satisfied are reversed shell/., in the 

 r ~*~ jn*"** as the other Plcuutrlx*, although the lower part of the 

 disk U almost flat and carinatod at its edge, and therefore bean a con- 

 siderable resemblance to the flattened spire of some land shells, 

 particularly the Jltlir albtlla. 



Mr. Sowerby thus defines the genus Planorlit : Shell discoid with a 

 depressed spire, whose apex is always distinct : its whorls turn from right 

 to left, so that when the spire is held upwards and the aperture seen, it 

 is on the left-hand side. The shells are vcutricose, frequently cari- 

 natrd, either above or below ; the aperture is entire, its breadth equal 

 to ita length, sometime* greater but (Mr. Sowerby believes) never lea; 

 sometime* the peritreme, or lip, is thickened and expanded, and its 

 lower part is always extended forwards : the umbilicus U very much 

 expanded, and there is no operculum. 



Mr. Sowerby further remarks that some specie*, particularly when 

 young, are covered with a hairy epidermis. 



M. Deshaye* (ed. Lamarck, torn, viii., 1833) does not make any allu- 

 (ion to Mr. Sowerby'i observations ; but he comes to a very different 

 conclusion. The Planarba, says he, as all naturalists know, are 

 discoid shells, generally delicate and fragile, found in abundance in 

 stagnant waters. Some of the species are so much flattened that they 

 seem perfectly symmetrical, so that it is difficult, in these last at 

 Inr*. to distinguish the upper surface from the lower. This difficulty 

 brings with it another, namely that of determining whether the 

 species are dextral or sinistraL These interesting questions had not 

 been deeply discussed when M. Desmoulins published (1831), in the 

 ' Transactions of the Linnean Society of Bordeaux,' a well executed 

 and very extensive memoir, in which be examines these different 

 questions. " In my preceding works," continues M. Deehayes, " I 



above, widely unibilieated beneath ; of a horny or brown-chestnut 

 colour ; the whorls transversely striated. 



questions. 

 have not 



_ave not perhaps attached sufficient importance to those researches 

 for which it was necessary to examine the living animals, but never- 

 theless in 1824 I disposed conchologically of a part of the difficulty 

 by laying, in my work on the fossils of the Paris basin, that the upper 

 side of the Plamrrbt* may be distinguished from the lower by means 

 of the obliquity of the aperture, the upper part of which is most 

 prominent (avancl). This mode of distinguishing the upper surface 

 bom UM lower, and of placing the shell in it* normal position, once 

 granted, it become* easy to recognise which species are dextral, and 

 which sinistral. By these means we perceive, as M. Desmoulins has 

 very well demonstrated, that nearly all the known species of Planorba, 

 both living and fossil, are dextral; even those which the most 

 teemed author* had judged to be sinixtral, from the depth of the 

 umbilicus. But if by the observation of the aperture we come to the 



conclusion that the shell of the Planorba is dextral, a difficulty pre- 

 sents iterlf, namely, that the animals which inhabit these dextral 

 shells ire sinistral, if we judge by the position of the three orifices 



' which the pnhnoniferou* mollusc* exhibit exteriorly. Thus Cuvier 

 has well remarked this transposition of the orifices in Planorbit 

 conttu, and ha* not hesitated to declare this species sinistral, con- 

 trary to the opinion of Linnaras, of M tiller, and of Draparnaud, who 

 state that UM species is umbilicated above. Cuvier corroborates his 

 opinion by an important fact, namely, that the heart is on the right 

 ids in Puutorbit, whilst it is on left in dextral shells of other genera ; 

 but Cuvier did not pay attention to the organs of digestion : finding 

 the heart on the right and the orifices on the left, he came to the con- 

 clusion that Planorba content is sinistral ; he ought nevertheless to 

 have se*ti, before he delivered this definite judgment, in what real 

 position the organs are. It is to this point that M. Desmoulins has 

 specially applied himself, and he saw that all the organs of digestion 

 and gmcration remain in the p titin which they hold in the doxtral 

 moHrnfl*, and that the orifice* only have an auormal position. Thus 

 UM observations of M. Deamoulins explain how, in the genus Planorbit, 

 appearancM place a sinwtral animal in a dextral shell (a phenomenon 

 which we cannot conoeivs) and how, in reality, the animal is dextra 

 a well a* it* shell, and that there is no other derangement in the 

 reMlonship of the** organs excepting in renrd to the heart, and the 

 termination of UM dig-tire organs and thoM of generation." 



The species are numerous. Lamarck recorded twelve recent species 

 including P. Con* An* it, which U not a Planorbu, but a discoid 

 AmpvUaria, as iu animal and operculum testify. M. Deshayes adds 

 ten more in the last edition of Lamarck; Conrad, Troschel, and 

 Brodsrip have each described one in addition ; and new species are 

 brought home by almost every expedition. M. Rang states that he 

 ha* known individuals of P. Itucottoma collected at Seise near Bor 

 tons, by M. Durie.i, where UM animals had closed the shell by a 

 kind of epiphragma analogous to that of the /feliet*. 

 P. cvnstM (/Mir conwo, Linn.). Shell opaque, piano-depressed 



Shell of Plaaorbit corncut. 



This, the largest living species of Europe, if not the largest 

 {enerally, is found in sluggish rivers and stagnant waters, such as old 

 water-courses and drains in low swampy (situations. Thus it is 

 plentiful about Oxford. Montagu says that it is certainly more local 

 ;hau it U described to be by Da Costa, who states that it is common 

 in all ponds, rivers, and lakes throughout England. This, adds 

 Montagu, is far from being the case, although it is sufficiently plen- 

 tiful in some parts, and be state* that he never found it further west- 

 ward than in Dorsetshire, where, about Wureham, it U abundant. 

 Lamarck records it as an inhabitant of France in the rivers, and very 

 common, about Paris, in that of Gobelins. 



Montagu, as well as others, have observed that this species yields a 

 beautiful purple dye (whence perhaps De Ferussac's name, P.purpura), 

 all attempts to fix which, either by acids or astringents, have hitherto 

 proved ineffectual. The inside of the mouth of the shell in fine 

 specimens is occasionally of a colour approaching to violet. 



Phyta. Animal of an oval form, more or less spiral; head 

 furnished with two long tentacles, which are setaceous and oculated 

 at their internal base ; mantle with two lobes digitated ou the edges, 

 which can be turned back so as to cover a considerable port of the 

 shell ; the foot is long, rounded anteriorly, pointed posteriorly ; the 

 rest of the organisation as in Limnaa, with the exception that the 

 orifices are generally on the left. 



Shell generally sinistral, oval, elongated or nearly globular, smooth, 

 delicate, and very fragile ; the aperture oval, a little narrowed behind ; 

 edge of the right lip sharp; columella a little twisted, but without any 

 plait ; spire more or leas sharp and elongated ; the last whorl larger 

 than all the others conjoined. (Rang.) 



Phyui. Shell and animal, with eggs. 

 a, rhyia kypnorvm ; fr, mau of eggt, natural sUc ; r, the same, magnified. 



The geographical distribution of the species is very extensive. 

 Species have already been found in the tranquil fresh waters of all 

 the four quarters of the globe. Europe has several species, and the 

 form occurs in America, in Africa (there being little doubt that the 

 Ilulin of Adanson is a Pliyia), in Australia, where it was found by 

 M. Quoy, and in the isles of Bourbon and 'Mauritius, whence it was 

 brought by M. Rang. Dr. Gray has named two species from the East 

 Indies and one from Peru. 



Mr. O. 11. Sowerby, as we have already seen, unites Phyta and 

 Limnaa, making the latter include the former for the reasons above 

 given. M. Rang, who notices their inhabiting the same places as the 

 Limntra,, and their resemblance in organisation, observes that the 

 animal of J'kyta is distinguished from that of Limnaa by the form of 

 ite tentacles, as is the shell by its generally sinistral disposition like 

 that of the Planortia. Ho also notices the observation of M. De Blain- 

 villc that there exist dextral species. 



M. Deshayes, in his edition of Lamarck, remarks that the genus 

 Phyia, established at first by Adanson under the name of Dulin, was 

 not definitely introduced till Draparnaud presented it anew under the 

 name which it still bears. Adanron, ho continues, had too much 

 nagacity not to perceive the relationship of his liulin with the 

 I'lanorlvt, and fails not to insist upon this point, although he 

 point* out the characteristic differences of the two genera. After 

 some observations on the doubts of naturalists as to the analogy 

 presented by the animals of Ptanorbii and those of Phyia and 

 Limnaa, and the absence of doubt as to the distinguishing characters 

 of the two last-mentioned genera, M. Deshaye* thus continues: 



