148 Memoirs of the Indian Museum. [Vol. VII, 



notch and the absence of an umbilicus, the latter, however, being a direct result of 

 the feeble depth of the terminal notch, the accretions to which consequently do not 

 produce the strongly twisted bulge, which leaves room for the formation of a more or 

 less developed umbilicus amongst the species referred to Dolium, s. str. Cossmann 

 also mentions, as a differential character, the tuberculation of the spire or body- 

 whorl, but as the genotype, Dolium crosseanum, is without tubercles, this character 

 cannot be strictly taken into consideration. 



If we ignore the depth of the terminal notch and the consequent presence or 

 absence of an umbilicus, we find, as regards the two other differentiating features, 

 namely the slight posterior channel and the rugose columella, that Dolium fasciatum, 

 D. zonatum and, amongst specimens of Dolium tesselatum, all those that are not 

 adult, agree with Eudolium rather than with Dolium, s. str. Moreover, leaving aside 

 again the fully adult specimens of Dolium tessellatum, these three, species are further 

 characterised by an internally thickened labrum with conspicuous denticulations, 

 usually bifid, which is not distinctly developed in any of the other species hitherto 

 referred to Dolium, s.^str., but which is invariably present in those that have been 

 referred to Eudolium, as well as in the sub-genus or genus Malea. 



If then we leave aside the characters furnished by the terminal notch and 

 umbilicus, Dolium fasciatum, D. zonatum and D. tessellatum will have to be regarded 

 as members of the group Eudolium, and, what the diagnosis loses in precision by the 

 exclusion of the umbilical characters, it gains to an extent at least equal by including 

 those of the outer lip. Now, the characters of the outer lip constitute precisely one 

 of the features in which Eudolium recalls the Cassididse, and, by adopting the 

 grouping here proposed, we moreover include within Eudolium precisely both those 

 species which occasionally exhibit a pre-apertural varix such as is observed in many 

 Cassididse. 



The tubercles observed on some fossil forms of Eudolium are derived from a 

 pronounced axial decoration analogous to the regularly distributed web of axial lines 

 that characterises Pirula. Just as the characters of the aperture have prompted the 

 erroneous reference of certain forms of Eudolium to the genus Cassidaria, so has this 

 reticulated or tuberculated ornamentation, especially when combined with the 

 elongate columella that distinguishes certain fossil forms, caused their erroneous 

 reference to Pirula. The earliest portion of the spire following the protoconch generally 

 shows a distinct web of regularly distributed lines of growth in most species of 

 Dolium : but this character is particularly well marked in the case, precisely of 

 Dolium fasciatum in which the axial lines are at first as thick as the average of the 

 spiral ornaments, with which they combine to form so characteristic a network that 

 the early part of the spire of Dolium fasciatum might be easily mistaken for that of 

 a Pirula (PI. ii, fig. 3c). 



According to Dall (Bull. Mus. Comp. Zool, 1889, Vol. XVIII, p. 223), the 

 radula of Dolium crosseanum resembles that of the Cassididse more than that of 

 Dolium, s. str. Apparently the only species of Dolium, s. str. of which the radula 

 has been figured is Dolium perdix (Troschel, Gebiss d. Schneck., Vol. I, pi. xix, 



