1919.] E. W. Vredenburg : Shells of the family Doliidœ. 161 



Height of body- (i) (2) (3) (4) (5) (6) (7) 



whorl . . 105 mm. 84 mm. 64 mm. 56 mm. 49 mm. 33 mm. 32 mm. 



The next specimen, of uncertain origin, is remarkable for its exceptionally 

 sunken spire : 



Height . . . . . . 70 mm. 



Thickness . . . . . . 58 ,, 



Height of spire . . . . . . 16 „ 



Height of body- whorl . . . . 65 ,, 



Variability and Development. — This shell is even more constant in its characters 

 than the previously described Dolium maculatum, the only distinctly variable features 

 being those of the colour scheme. As regards the more essential characters, one 

 merely observes slight differences in the more or less sunken disposition of the spire, 

 and the more or less distinctly spherical or ovoid outline of the body-whorl. 



At the same time, some very remarkable differences are observed in the appear- 

 ance of the shell at different stages of growth, especially with reference to the aper- 

 tural characters. While, in the case of fully adult specimens, the aperture is pos- 

 teriorly simple, the outer lip undifferentiated, and the columella smooth, the shell at 

 early and intermediate stages of growth has a strongly fimbriate and denticulate 

 outer lip, a posteriorly slightly channelled aperture, and a distinctly rugose columella. 

 Whilst the adult shell is in every sense a typical Dolium,, the posterior channel and 

 especially the rugose columella of the immature specimens recall the sub-genus 

 Eudolium. The external and internal thickenings, marginal fimbriations, and inter- 

 nal denticulations of the aperture, the posterior apertural channel, the thickening of 

 the columellar lip and the rugosities of the columella observed in these immature 

 specimens of Dolium tessellatum agree in every respect with the corresponding fea- 

 tures observed at all stages of growth in Dolium fasciatum (Brug.) which there is 

 reason to refer to the subgenus Eudolium, and readily account for Kiener's interpreta- 

 tion of such specimens of Dolium tessellatum as representing a variety of Dolium 

 fasciatum. The development of Dolium tessellatum is of great interest as suggesting 

 the possible derivation of the more typical forms of Dolium from Eudolium, especial- 

 ly as, so far as can be judged from the information at present available, Eudolium is 

 geologically more ancient. 



Occurrence. — With the exception of a few individuals of uncertain origin, all the 

 specimens in the collection of the Indian Museum are from the Andamans and 

 Nicobars. Shells certainly referable to this species have been obtained from the 

 Malay Islands and Japan. 



In a fossil condition, the species is known from the upper miocène and pliocene 

 of Java, and from the pliocene of the Mekran. 



COMPARISON OF DOLIUM MACULATUM AND DOLIUM TESSELLATUM. 

 Remarks on the Taxonomy. — Owing to the hopelessly confused synonymy of the 

 forms under consideration, the task of discovering suitable names for the two species 

 above described has proved extraordinarily troublesome. 



