606 MR. H. F. BLANFORD ON THE DESCRIBED FORMS OF TANALIA. 
to locality, I found that specimens from the same stream, and collected on the same spot, 
were in all cases somewhat variahle, and sometimes exhibited a considerable range of 
variation — moreover that, however great this range, the local series presented a perfect 
gradation between the extreme forms. Thus, in the Kelany Ganga, between Kitoolgalle 
and Yatteantotte, while the majority of the specimens were of the form T. Tennentii, 
frequently with the colour and markings of T, picta, some few occurred of the var, 
T. undulata (having, however, spiny instead of nodular ribs) ; and linking these together 
were specimens of the type T. Gardneri with depressed and exserted spires, and T. undu- 
lata of the normal form, with other intermediate forms of minor gradation. In the Maha- 
velli Ganga, where all my specimens were collected within the space of a few yards, the 
shells exhibited but a small range of form and sculp hire, including the varieties T. picta, 
T. dromedaria, and T. neritoides ; but the size of fully grown specimens ranged from 9J 
lines to 15 lines in height, and from 10 lines to 14| lines in the major diameter. A series 
of measurements of specimens from this collection is given at p. 609. Minor variations 
of ribbing and colour were also observable. 
Finding thus that the species is evidently a very variable one, I selected, from Major 
Skinner's and from my own more limited collection, series exhibiting the ranges of varia- 
tion in the following characters : 
1. Ornament of sculpture, 
2. Colouring, 
3. Exsertion of the spire, 
4>. Size of specimens, 
on each of which a few words are necessary. 
Some other characters are also variable, such as the form of the operculum (see ante, 
p. 605) and the excavation of the upper part of the whorl ; but the above are more 
important, and to them I shall confine my remarks, contenting myself with the passing 
assurance that the two last mentioned are far too inconstant in their relations to other 
variations to allow of their being admitted for an instant as specific distinctions. 
1. Sculpture. 
The varieties T. Tennentii or T. dromedaria and T. Skmneri or T. erinacea exhibit 
respectively the extreme varieties of sculpture. Between these types I have a series of 
twelve intermediate forms*, illustrating the gradual appearance and development of 
ribs, and the breaking up of these ribs into nodules, which finally in the two last- 
mentioned forms are exaggerated into scale-like spines f . 
Even in the smoothest specimens (Fig. 1, T. Tennentii) faint indications of the spiral 
ribs may be noticed, as well as striae of growth : the most common variety is perhaps that 
which has distinct but not highly developed subequal ribs (Fig. 2). As these become 
* Six of these are given in the accompanying Plate, Series I . 
with a series 
peristome, in which, when the animal 
Th 
with 
N[ 
