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 variable, 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. imchilata (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. tindu- 

 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 oiform and sculpture, including the varieties T. picta, 

 T. dromedaria, and T. neritoides ; but the size of fully grown specimens ranged from 9^ 

 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. Skinneri 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 t- 



Even in the smoothest specimens (Fig. 1, T. Tennentii) faint indications of the spiral 

 ribs may be noticed, as well as strise 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. 



t The ribs of the shell of Tanalia .correspond with a series of indentations on the edge of the external lip of the 

 peristome, in which, when the animal is extruded, rest the fringes of the dorsal fold of the mantle. The number 

 and relative size of the ribs and notches correspond with those of the filaments. 



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