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



the shell is entirely known, the apertural denticulations and the collumellar rugosities 

 disappear in the case of thoroughly adult individuals, the species establishing there- 

 fore somewhat of a link between Dolium, s. str. and Eudolium. 



In those forms of which the apertural details are known the denticulations are 

 bifid. The forms which may be either definitely or provisionally classified in this 

 group are the following : — 



Dolium tessellatum, Bruguière, in which conspicuous intercalary ribs appear only 

 in fully adult shells. 



Dolium ormarense, Vred-, fossil, in which conspicuous intercalary ribs are seen at 

 every stage of growth ; Dolium costatum var. martini, Boettger (Die Tertiaer formation 

 von Sumatra und ihre Thierreste, Part II, p. 84, pi. vi, figs. 4, 5, Palaeontographica, 

 Suppl., Vol. Ill) being perhaps identical. 



Dolium hochstetteri, Martin (Samml. des geol. Reichs-Museums in Leiden, new 

 series, Vol. I, p. 162), characterised, by its extremely depressed spire and posteriorly 

 inflated body-whorl. The details of the aperture are not known, and the classifica- 

 tion of this shell is therefore provisional. 



Dolium arabicum, Vred., fossil, characterised by the irregular distribution of the 

 ribs on the body-whorl; D. townsendi, Newton (Geol. Mag., dec. 5, Vol. II, p. 301), 

 being probably identical. As in the case of the preceding species the details of the 

 aperture are not known and the classification of the shell is likewise provisional. 



5th Division. 



In this division, which may be distinguished as the group of Dolium fasciatum, 

 the shell is umbilicated, the ribs are crowded and close-set, the denticulations bifid. 

 It includes the following species :— 



Dolium, fasciatum (Bruguière), in which the body-whorl is practically destitute of 

 intercalary ribbing, and the outer lip thickened both internally and externally. 



Dolium zonatum, Green, in which all the intervals carry intercalary threads and 

 the labrum is thickened only internally. 



6th Division. 



The shells of this division, which may be distinguished as the group of Dolium 

 crosseanum., differ from those of the preceding group merely in the absence of an 

 umbilicus. The denticulations are similarly bifid. This group includes the following 

 species : — 



Dolium crosseanum, Monterosato, the genotype of Doliopsis, Monterosato and of 

 Eudolium, Dall, characterised principally by its crowded spiral ornamentation closely 

 resembling that of Dolium zonatum. 



Dolium cinguliferum (Brown) (= D. fasciatum, Borson, non Bruguière), fossil, of 

 smaller size, with fewer primary ribs. 



Dolium muticum, Michelotti, fossil, strongly tuberculate, with labrum thickened 

 externally as well as internally. 



