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



The presence of Eudolium, as here defined, in the oligocène of Europe, while, in 

 the Eastern Seas, it is only known from upper miocène to recent times, and the 

 occurrence of Malea exclusively as a fossil in Europe, exclusively as a living group in 

 the Indo-Pacific, are typical instances of a large number of similar cases which at one 

 time were thought to imply an easterly migration of the tertiary fauna of Europe 

 into the Indo-Pacific region of the present day. It has now been shown that the 

 great majority of these cases resulted from our hitherto deficient knowledge of the 

 fossil contents of the tertiary formations of Asia, and, with increasing research, most 

 of these supposed instances have now vanished. 



It is clear, however, that amongst the minor divisions enumerated in the pre- 

 ceding list some have a well-defined geographical as well as geological distribution, 

 The most archaic group, that of Dolium crosseanum, is entirely restricted at the 

 present day as well as in former geological times to the Mediterranean and Atlantic 

 region. It is, so far as our present information goes, the geologically oldest group, 

 and that from which the other forms of Dolium seem to have been derived. It is 

 possible therefore that the genus Dolium may truly have had a western origin. 

 Dolium, s. str., as here understood, has not been found in a fossil condition in the 

 west. Dolium galea is special to the Mediterranean and Atlantic. The other forms of 

 Dolium, s. str., as here understood, are essentially Indo-Pacific, though Dolium perdix 

 has also spread to the West- Indies and to the coast of Brazil, evidently through the 

 former marine connection across Central America which has afforded a passage to 

 other Indian species, either still living in the Indian region, or known in a fossil con- 

 dition, as has already been pointed out in the publications of this Department 

 (Memoirs of the Indian Museum, Volume VI, p. 124). 



As already pointed out by Sacco (Moll, dei terr. terz. del Piemonte e della Liguria, 

 Part VIII, 1891, p. 22), the occurrence throughout the pliocene of southern Europe 

 of a Malea closely related to the tropical Dolium (Malea) pomum indicates the persis- 

 tence, in the Mediterranean region, of a warm climate down to the very eve of the 

 Glacial Epoch. 



Amongst the additions to our knowledge of the distribution of these shells 

 furnished by the Calcutta collection, one of the most interesting is that concerning 

 the presence, at Maskat, of Dolium variegatum, hitherto only known from the Austra- 

 lian region and Japan. While there is every reason to believe that the distribution 

 of Dolium variegatum at the present day is discontinuous, its occurrence in a fossil 

 condition in the Mekran beds as also in Java furnishes an easy clue to its present 

 occurrences, the distribution of the shell having been more extensive in former geological 

 times than at the present day. Another species, Dolium tessellatum which, at the 

 present day, does not appear to extend further west than the eastern part of the Bay 

 of Bengal, also occurs in a fossil condition in the Mekran region. Just as in the case 

 of Dolium variegatum, it seems now to have disappeared from the shores of the Indian 

 Peninsula, only, unlike D. variegatum, it has also disappeared from the northern 

 shores of the Arabian Sea. Consequently D. tessellatum does not exhibit at the 

 present day the discontinuous distribution observed in the case of Dolium variegatum. 



