330 NOTES ON PROSOBRANCHIATA, IV.^ 



not older than the veloconch, that the nepioconch was very pro- 

 bably not formed, and that the whole of the coiled portion is 

 ananeanoconch. If the nepioconch is present, it is represented 

 by the earliest of the coiled whorls. 



From the large size and very slight excentricity of the extreme 

 apex (which consists of phyloconch (?) and veloconch) it may be 

 inferred that the trochosphere was large, since excentricity of 

 growth commences very shortly after that stage, and the 

 symmetrical portion was probably moulded on the late trocho- 

 sphere or early veliger, and the early veliger could hardly have 

 been large had not the preceding stage been correspondingly 

 large. From the absence of a nepioconch I deduce a poor 

 development of the velum, because the absence of nepioconch 

 probably indicates a very brief nepionic stage {vide 4). Finally, 

 in the large size of the mollusc at the time of its escape from the 

 capsule we have certain evidence that there was no free-swimming 

 stage. Thus if, as I trust they are, my interpretations be 

 correct, we are able to briefly outline the later embryonic history 

 of a mollusc from its protoconch, and to this extent embryology 

 is placed within the range of palseomalacology. 



The section may be fittingly concluded by the following quota- 

 tion from Lankester — " .... we may speak of primary, 

 secondary, and tertiary shells in Mollusca, recognising the fact 

 that they may be merely phases fused by continuity of growth 

 so as to form but one shell, or that, in other cases, they 7nay 

 be presented to us as separate individual things, in virtue of the 

 non-development of the later phases, or in virtue of sudden 

 changes in the activity of the mantle-surface causing the shedding 

 or disappearance of one phase of shell-formation before a later 

 one is entered upon. "(6) 



iii. — The Naticoid Initial Whorl. 



In the paper above referred to (1) Grabau concludes that, 

 because the initial whorl of many Gastropods was smooth, 

 rounded and umbilicate, the Gastropod radicle was of this 

 " naticoid " character. The conclusion is ver}' tempting, but it 



