INTRODUCTION. 



however, exceptions to tliis, and correlatively it may be noted that 

 the shape of the protoconch occasionally determines the general 

 shape of the shell. In Bathytoma angustifrons (p. 49), for instance, 

 the Museum specimens show that the elevation or depression (as 

 the case may be) of the turns of the protoconch to a large extent 

 determines the relative elongation of the growth of the whole shell, 

 in that particular species. 



Evidence is given (pp. 95, 96, and description of the species 

 of Scaphella) that some of the Australasian Tertiary Volutid^ 

 possessed horny protoconehs ; and the classification of that family 

 as deduced from a study of the larval shells, together with some 

 account of the origin and development of the groups they represent, 

 will be found (p. 92 et sqq.). Cf. Fusus hezagonalis (p. 131) in 

 this connection. 



The ontogeny of Mitra multisiilcata (p. 120) forms an interesting 

 study. As a result of the details of gi'owth, it is shown that the 

 number of columellar plications is not necessarily of value in 

 classification in such a genus as Mitra ; for in the brephic stage 

 there were only two plaits, and the suspicion of a third, whilst 

 in the ephebic no fewer than five are observable. 



A very remarkable mode of growth is recorded in reference to 

 Tylospira coronata (p. 222) ; whilst Cerithium apheles (p. 224) 

 is full of interest. The shell in the latter exhibits longitudinal 

 costfe in the brephic stage, which are lost in the neanic, but 

 reappear strongly in the ephebic, only to die out again in the 

 gerontic stage. There is thus a high possibility of this species 

 having descended from a well-marked longitudinally costate stock, 

 with a tendency for its descendants to assume a much plainer type 

 of ornament. 



I have stated in an earlier part of this Introduction that, although 

 it is generally understood that during the brephic stage of growth 

 no specific characters can be distinguished, it was desirable to 

 discuss the matter. Some of the observations just made prove that 

 the shell is often highly sculptured in that stage, and many other 

 examples are recorded in the text. It is by no means rare to find 

 that the chief ornament relied upon for the classification of the 

 species (in regard to individuals) suddenly makes its appearance 

 in the brepliic stage, and, not infrequently, starts abruptly from 

 the termination of the protoconch. A glance through the plates 

 accompanying this work will, perhaps, help to make this observation 



