C O N C H O L O G Y. 



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extremely rational change has taken place Since the 

 revision of the Limuean school ; and it is now the 

 more useful, as it tends to facilitate naturally the 

 connection we deem inseparable of the animal and its 

 dwelling, which forms the leading feature of the 

 science of Malacology. Our present object is, how- 

 ever, confined, as we have already premised, to the 

 shells themselves, as detached portions ; and before 

 we proceed to the nomenclature of the science, the 

 following easy guide should be well retained in the 

 student's memory. It will be the more readily 

 understood by an examination of the accompanying 

 descriptive figure ; or we may at any time observe 

 the march of our garden snail as a living guide to the 

 subject. In uniAlve shells, it is easily conceived 

 that they must have had a point or portion from 

 whence they progressed in growth, a base which is 

 its actual termination in its final stages of increase, 

 or in its adult state of maturity, with an intermediate 

 state between these, which may be called the body 

 of the shell. This portion sometimes possesses an 

 almost imperceptible cavity in such as are extremely 

 depressed, or altogether flat, in which they partake 

 greatly of the character of one valve of a bivalve 

 mollusc. 



PLRITROTOMA BABTLONICA a, the canal j 6, the nearly closed 

 umbilica; c, the left or intestinal edge or lip; d, the right or 

 external lip; e, the notch or slit; /, the sinus ; g, the belly; 

 h, the turns or whorls of the spire ; i, the sutures. 



Linnaeus, of the old, and Lamarck, of the modern 

 school, placed the shell they were about to describe 

 on the opposite extremity to the summit, its only 

 natural position when separated from the animal, but 

 with the aperture fronting the spectator. Modern 

 naturalists, on the contrary, place the shell as it is 

 found on the animal when proceeding on its march, 

 that is, with the spire towards the observer, the 

 summit consequently upwards and behind, and the 

 opposite portion, or the base, as it is generally called, 



in front and beneath. In this mode of examining a 

 shell, it is clear that the right and left side app.y 

 equally ; but the one so called by Linnaeus is now, 

 by reversing the position of the shell, exactly the 

 contrary of modern authors. The right of the old 

 system is the left of the modern, and vice versa. The 

 terms, inferior siid xttpcrior, in the description of the 

 aperture and its edges, are necessarily replaced by 

 the terms, anterior for the first, and posterior for the 

 second. The apex, or summit, is that part from 

 whence the shell first proceeds, or, more properly, it 

 is the commencement of the spire. This portion may 

 be altogether flat, or very salient, straight or vertical, 

 or directly leaning backward, to the right or to the 

 left, or even forward. It may be pointed, mamillated, 

 entire or carious, and even sometimes hollow, as in 

 the Bulla. Thus the summit is altogether planus, or 

 flat, as in the Chinese limpet ; peracuttts, or very 

 salient, as in the Vermetus ; verticalis or vertical, as in 

 the Patella or limpet, whence Linnaeus has called it 

 (vertex;) narginalis, and sub-marginalis, as in the 

 Crepidula ; rctroversus, depressed backward, as in the 

 Navicella ; aiitcversus, the converse to the latter 

 position, as in certain species of Patella, and, above 

 all, in the Emargiiwla ; sinistralis, or left-handed, as 

 in the Ancylut ; dextralis, as in the Capulus ; acutus, 

 pointed, as in a great number of shells ; mamillaris, 

 mamillated, or rounded, as in the Volutes ; integer, or 

 entire, as in the greater portion of shells ; cariosus, 

 eroded, or carious, as in the Bulinus ihiara ; tnmcattts, 

 or decollatus, as in the truncated Bitlinus, and several 

 other species of turriculated mojluscs ; umbilicatus, 

 utnbilicated, hollowed, sunk in, as with the Ihtlhi and 

 their congeners, as also with certain species of 

 Ammonites and Planorbis, but then the pex is lateral ; 

 tcrcbratus, pierced, as in the Dentulium. Basis, or 

 the base of a shell, is that part which is usually 

 opposed to the summit, and in which the aperture is 

 formed. Under this name, however, \ve do not 

 understand that which Linntcus and his disciples have 

 designated as the base of a shell ; for in fact, accord- 

 ing to their view, it is the extremity, pointed or not, 

 which is opposite to the summit, and they made it 

 so, because, according to their method of designating 

 the different parts of shells, they placed this one ver- 

 tically, the summit above and the aperture behind. 

 In the present school, the base comprehends all that 

 part which rests more or less obliquely on the back 

 of the animal. Sometimes this base is very large 

 and round, amp/a, rotunda, as in the Trochus, which 

 gives them the form of a reversed one ; sometimes 

 it is parva, small, as in the Tcrebra, Subula, &c. It 

 may be extremely elongated, elongata, as in the 

 Cyprcea, &c. ; and it is formed entirely by the 

 aperture, as in the Pate/la sigaretus ; but many other 

 molluscs more frequently have their base formed by 

 a portion of the last turn of the spire. 



The direction of the base, which is usually in that 

 of the opening, also offers some considerations 

 deserving notice ; it is altogether perpendicular to 

 the imaginary axis of the shell in the Patella, 

 Solarium, &c. ; it is almost entirely in that of the 

 aperture in the Oliva, Cyprcca, &c. ; in other shells, it 

 is more or less intermediate. 



That portion of shells termed the body occupies 

 the whole space between the summit and the base. 

 It is most frequently hollow, and not only serves as a 

 covering, but also contains the whole, or a part of the 

 animal's body. 



