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n 
more strongly marked (Fig. 3, T. Gardner}), the alternate ribs are more developed 
and those intervening narrow and filiform. In the next stages, the alternate ribs, or ii 
some specimens all the ribs, become undulated (Pig. 1), then nodular, the nodules being first 
small and close (Fig. 5), and afterwards more distant and prominent (Fig. 6, T. lor 
from which the passage into T. Skinneri and T. erinaeea consists in, first, some of tin- 
spines, and finally all, remaining unfilled and in the form of scales as they first appear at 
the edge of the shell. The varieties T. area, T. Layardi, T. Reevei, and T.fniiculotc 
differ from T. Gardneri chiefly in the elevation of the spire and the greater and regular 
development of the striae of growth. These forms (as has been remarked by Mr. Layard 
in the case of the two first mentioned) pass into T. undulate, and this again into T. 
with an elevated spir 
2. Colouring. 
-« 
When taken from the water, most specimens are more or le^s covered with adherii 
Algae, which require soap and water and a stiff brush for (heir removal. "When thus 
cleaned, the epidermis is seen to be of a rich brown colour, varying from a pale yellow 
brown to a tint bordering on black. Beneath this, the proper colouring of the shell is 
always perceptible in young specimens, and frequently also in old. It is very clearly seen 
in the variety picta, which has a thin epidermis, and in which it assumes the form of 
waved transverse bands varying in closeness and regularity, being sometimes so irregular 
as to simulate a reticulate marbling. The variety T. Tennentii, from Ambegammoa, is 
frequently marked in a similar manner. This is the commonest type of colouring in all 
varieties ; the only modification of it I have observed is that in which the transverse 
bands become more or less interrupted, but regularly(as in JP. chiUnoides), so as to form 
spiral bands of zigzags. This is chiefly observable towards the aperture of full-grown 
specimens, the young part of the shell having the normal colouring. I have met also 
with a few cases in which the shell was colourless near the aperture. 
The painting of the peristome varies but little. The inner lip is coloured purplish 
brown ; and the tint sometimes extends round the outer lip also : it is the colour of the 
callous deposit which strengthens the aperture of full-grown shells. Very frequently a 
series of brown dots also ornaments the edge of the outer lip, being the tips of the zigzag 
markings appearing beneath the callus. In old specimens this callus, the internal part 
of which is white or brown, or white blotched with brown, extends far into the shell, 
obscuring its zigzag markings. These remarks apply to all forms of Tana Ha here 
included under T. aculeata. 
3. Form of Whorls, and Exsertion of the Spire. 
The form of the whorl varies but little throughout the species : it is always obliquely 
flattened above, and in some specimens (var. dromedaria, e. g.) this feature is exaggerated 
into a slight excavation of the whorl near the suture. The ribbed and nodulose varieties 
differ in this respect as much as the smooth forms. The dilatation, or, in other words, the 
ratio of increase in the growth, of the whorls varies also in all varieties. The form of the 
spire is very inconstant : it is sometimes as much exserted as in a typical Paludina (e. g. 
VOL. XXIII. 
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