Zoological Illustrations/VolI-Pl36

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Zoological Illustrations
by William Swainson
Vol I. Pl. 36. Achatina perversa. Reverse Achatina.
Zoological Illustrations Volume I Plate 36.jpg

ACHATINA perversa.

Reverse Achatina.

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Generic Character.—See Pl. 30.

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Specific Character.

A. (Div. 2.) testâ aperturâ perversâ: spirâ productâ, 7-volutâ, apice truncato; albida strigis nebulosis cinereis; linea transversa in basali anfractu; columella margineque labii exterioris castaneis, apertura intus alba.
Aperture reversed: spire lengthened, of seven volutions, the apex truncated, whiteish with clouded cinereous stripes; central band on the basal volution, pillar, and margin of the outer lip chesnut; mouth within white.
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Reverse shells, or such whose mouth when viewed in front is on the left side, are generally held in much estimation by collectors. This deviation from the usual form of shells is sometimes accidental, as in our common garden Snail and several others; while in some species it appears a constant, and therefore a specific distinction. Such I apprehend is the case with the shell now figured, a rare and very elegant species, apparently not noticed by any writer; two or three existing in the British Museum and one in my father's cabinet are all the specimens I have hitherto seen. The latter (here figured) came from Bahia in South America. The whole shell is very finely marked with longitudinal striæ, and the colouring better seen than described: the buff tinge at the base is occasioned by the remaining epidermis.

This shell belongs to the second division of the genus Achatina as mentioned at Plate 30, having the aperture much shorter than the spire and the base nearly entire. Bulla virginea of Linn. seems to connect the two divisions, having the lengthened spire of one and the truncated base of the other.