709 



THE PROTOCONCHS OF CERTAIN PORT JACKSON 

 GASTEROPODA. 



By H. Leighton Kesteven. 



(Plates xxxv.-xxxvi.) 



In the "Catalogue of Tertiary Mollusca in the British Museum'^ 

 (Introduction, p. xiv.) Harris sa3^s : — " I have found that the 

 greatest difficulty in defining the brephic [or nepionic] stage is in 

 those cases where a strong varix has been thrown up at the con- 

 clusion of the embryonic stage, and it seems right that this should 

 be so. For the varix certainly indicates a pause in the grotvth of 

 the shell, and it is reasonable to suppose that during that pause the 

 animal toas passing through the brephic stage, but did not continue- 

 to make the normal shell of that period, except partially, it may 

 be, in some instances. I have even doubted Avhether in certain 

 instances the varix alluded to was not, in fact, the only manifesta- 

 tion of the growth of the shell during the brephic [or nepionic] stage." 

 The italics in both instances are mine. 



In some of the shells discussed here, especially Murex australis, 

 the sculpture of the shell which follows the "varix thrown up at 

 the conclusion of the embryonic stage " is, in miniature, that of 

 the adult. The original of tig. 11, pi. xxxv., is on that account 

 identifiable without obtaining a series. 



The auxological terms of Professor A. Hyatt apply to morpho- 

 logical not conchological periods of "growth. That being so, it 

 seems to the writer that the nepionic stage of the marine Gastero- 

 poda may be defined thus: — that stage in which the embryo, having 

 reached its full development, loses its embryonic characters and 

 assumes its adult form. If this be right, that there should be a 

 pause in the growth of the shell is only natural, and I would 



