Zoological Illustrations/VolI-Pl30

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Zoological Illustrations Volume I Plate 30.jpg

ACHATINA marginata.

Marginated Achatina.

Generic Character.

Testa ovata, vel oblongo-ovata, spira elevata, apertura subovale. Columella lævis, simplex, ad apicem truncata; labium externum tenue, internum inflexum integrum; umbilicus nullus.

Typus Genericus Bulla Achatina. Linn.

Shell ovate, or oblong-ovate; spire elevated; mouth nearly oval. Columella smooth, simple, truncated. Outer lip thin; inner lip entirely inflexed. Umbilicus none.

Generic Type Bulla Achatina. Linn.

Specific Character.

A. testa ovato-oblonga, strigis inæqualibus ferrugineis; spira ad apicem obtusa, 5-voluta; sutura depressa linea sulcata marginali.
Shell ovate-oblong, with irregular ferrugineous stripes; spire obtuse at the top, of five volutions; the suture depressed, with a marginal indented line.
Lister 579. fig. 34. Gualt. pl. 45. B. Knorr, vol. iv. tab. 24. 1. (badly coloured.)

The largest shells hitherto discovered as inhabiting the dry land belong to this genus, instituted by the celebrated Lamarck, but still divided by the strict followers of Linnæus between the Bullæ and Helices, with a singular infelicity of even artificial arrangement. The simple characters peculiar in a greater or less degree to all, will readily distinguish them; and I apprehend most of the species of the first division (which includes the present) will be found to inhabit only the African continent, while Bulla virginea and the smaller shells placed in the second division are found principally in the new world; where also two or three gigantic species of Bulimus occupy the place of the larger African Achatinæ.

Of these, the shell now figured is one of the rarest, and has hitherto been overlooked as a variety of the Linnæan Bulla Achatina; the colour of both is subject to much variation; but this will be found at best a most indecisive and vague character for specific distinction when unaccompanied by others more important and connected with the formation of shells. I have therefore not hesitated in making this a distinct species, from having had the means of examining at different times near twenty specimens, all of which presented the following characters. Spire of five whorls, the last or terminal one very small and flattened; the apex obtuse; the suture depressed, as if flattened on the shell, and margined by one or sometimes two indented lines, parallel, and at the top of each whorl. In the colour of its mouth it varies in sometimes having a tinge of rose-colour at the base and top of the spire, but the mouth is more generally white. The body whorl is more or less ventricose; the outer lip is a little reflected, and the whole shell, when full grown, much thicker and heavier than any of the other species. The epidermis is yellowish-brown, beneath which the shell is nearly white, beautifully marked with broad remote stripes of chesnut, with others more slender (and sometimes broken into spots) between. I have another specimen which agrees tolerably with Lister's figure in being more than usually ventricose, and which I think is accidental. The only constant variety appears to be that figured by Knorr, ii. tab. 3. fig. 1. having the spire entirely rose-colour.

The marginal line and the correct number of whorls in the spire are well expressed in the figures of Lister, Gualtieri and Knorr. The first of these figures is accidentally more ventricose; the second, like all the other figures of Gualtieri, is defective at the apex; and Knorr's I suspect has been outrageously coloured from the real pink-mouthed Achatina.

It inhabits the coast of Guinea; and I am informed the animal is eaten by the natives.