1919. J E. W. Vredenbürg : Shells of the family Doliidœ. 171 



Fifthly. The columella of Dolium tessellatum is shorter than that of DoUum 

 maculatum. Except in the case of very large, quite adult specimens, it is always 

 rugose in the case of Dolium tessellatum, while it is smooth at all stages of growth in 

 the case of Dolium maculatum. 



Sixthly. The vast majority of specimens of Dolium maculatum of all sizes have 

 a perfectly simple outer lip. When the outer lip is at all differentiated, it is feebly 

 expanded externally, feebly thickened and non-denticulate internally, with a more 

 or less wavy, feebly fimbriated edge. In the case of Dolium tessellatum the outer lip 

 is invariably differentiated, its special characteristics, in the case of the largest fully 

 adult specimens, being reduced to a mere internal thickening, while in every specimen 

 of small or medium size it is externally expanded, internally thickened and denticu- 

 late, and is conspicuously fimbriated all along the edge. 



In conclusion, the differences are amply sufficient to justify the reference of 

 both forms to totally distinct species which are not even closely related. The simpli- 

 fication of the aperture in fully adult specimens of Dolium tessellatum,, combined with 

 the adult reappearance of an intercalary sculpture, taken in connection with the 

 adult broadening of the intercalary ribs usually observed in Dolium maculatum, gives 

 rise to a deceptive suggestion of convergence which, nevertheless, is quite superficial. 

 The history of the development of both shells clearly shows how widely divergent are 

 their zoological affinities. 



Affinities of the two species. — Dolium maculatum appears to be an isolated species 

 amongst the recent fauna, and is not closely related to any other known living form. 

 In the characters of the outer lip, of the columella and of the umbilicus it distinctly 

 recalls Dolium galea, the type of the genus, as well as the closely related Dolium 

 melanostoma, Jay and D. variegaturn, Lam., but is clearly separated by the wide-spaced 

 disposition of the primary ribs which, on the contrary, are close-set in Dolium galea 

 and the related forms. In any case Dolium maculatum is to be classified as a typical 

 Dolium. 



Dolium tessellatum, if we leave out of account the fully adult or gerontic indi- 

 viduals, is undoubtedly closely related to Dolium fasciatum, Brug., with which it 

 agrees as regards the posteriorly channelled aperture, the rugose columella, the 

 externally and internally thickened, denticulate and fimbriate outer lip, being dis- 

 tinguished only by the somewhat less ovoid outline of the body-whorl, and the 

 smaller number and wider spacing of the primary ribs, as well as some differences in 

 the colour decoration. It also shows a relationship though more distant to Dolium 

 zonatum, Green. In their apertural characters, Dolium fasciatum and D. zonatum 

 correspond so closely with Dolium crosseanum, Mont., the type of Eudolium, as to 

 justify their inclusion within that subgenus or section ; the exact classificatory posi- 

 tion of Dolium tessellatum being rendered thereby, as already mentioned, somewhat 

 uncertain, since it may be regarded as a Eudolium when immature, a Dolium, s. str. 

 when full grown. It is clearly at the mutual limit of the two groups, and indicates 

 how feebly defined is their separation. 



The pliocene beds of the Mekran contain an extinct species which has provision- 



