INTRODUCTION. IX 



consideration. As a further illustration T may refer to p. 9G, 

 "where, after giving some account of the larval shells of the 

 VoLUTiDJK (p. 92 et sqq.) and the light they throw on the origin 

 and evolution of that family, I state that tlie development of these 

 larval Volutes in the majority of instances in specimens found at 

 the localities mentioned .... is much more advanced than 

 one would have expected to find in beds as old as the Eocene — that 

 is, on comparison with what is found in the true Eocene in other 

 parts of the world. And it would not be difficult to give other 

 evidence of the same nature. No doubt some families make more 

 rapid strides in one area than in another ; but it is surprising to 

 find in the Gasteropoda how uniform over large areas the rate of 

 progression has been in regard to many of the widely distributed 

 families. There is, for example, the genus that has survived from 

 early Mesozoic times, with hut little modification in the later stages 

 of its journey ; it has had its day, and has settled down as a more 

 or less fixed form. Such a genus is of little use for homotaxial 

 purposes, though eminently interesting from a purely phylogenetic 

 point of view. What we want to study specially for the purposes 

 of Tertiary homotaxis are those families, quite numerous enough, 

 the chief members of which, having parted from the main stock 

 in late Jurassic or Cretaceous times, arrive in the Eocene, with 

 strong tendencies to variation, and, at the same time, are rapid 

 travellers and become ubic|uitous, as is the case with many 

 prominent genera of the Australasian Tertiary Gasteropoda. But 

 this is not the place to enlarge on the value of phylogeny to 

 the geologist, and the subject is introduced here only as in some 

 measure the outcome of a study of the Tertiary MoUusca from the 

 Antipodes now catalogued. 



In the foregoing observations special stress has been laid 

 on the study of Gasteeopoda, but it must not be understood 

 that the fossil Lamellibeanchiata are one whit inferior in 

 point of interest from the phylogenetic or the geological stand- 

 point. The want of sufficient suitable material in the Museum 

 for the study of the auxology of the Australasian Tertiary 

 LAMELLiBEAXcniATA, is the sole cause for the omission. It should, 

 however, be added that in many specimens the prodissoconch is 

 excellently preserved. 



The n.imes employed to designate stages of growth of the 

 individual, and the sense in which they are applied in this work, 



