BY H. L. KESTEVKN. 75 



form has evolved from the Tertiary by the continuous tachy- 

 genetic inheritance of this reduction in the power to form a 

 heavily sculptured shell. (C ■parkinsonianuiii is the recent 

 species I associated with C . radialt Tate, 6'. ioi-flrostris Tate, 

 C. (ibbofi Tate, C texdle Tate, and C woodsi Tate, and all 

 have the same contour and general appearance as the three 

 figured here.) 



The general conclusions arrived at are : — 



1. The Gastropod Protoconch may have been formed during 

 one or more of four stages in the ontogeny of the mollusc- 



2. The common practice of speaking of the early portion 

 of the true conch as N eywnic, is wrong ; it would be more 

 correctly designated Ananeamc. 



3. The JVepionic stage in the Mollusca, at least in the Gas- 

 tropods, is exceedingly brief ; and, in the great majority of 

 cases, leaves no conchylaceous record. 



4. As a taxonomic feature, the protoconch is practically 

 worthless, and is liable to be, and inded has proven, very 

 misleading. 



5. This is owing to the fact that its various forms have 

 arisen from factors other than phylogenetic. 



6. The absence of definite types of Yeliger larvae corres- 

 ponding to the main divisions of the Gastropoda, is very 

 strong evidence that phylogenetic factors have not acted upon 

 this stage of the gastropod ontogeny (and it is during this 

 stage that the vast majority of protoconchs are formed)- 



7. By reference to phenomena observed (and more or less 

 explicable) in other Phyla, much light is thrown upon the 

 variations of the Gastropod Protoconch. 



8. The Heterostrophe apex has arisen from two factors : 

 {fi) the initial sinistral coil ; (6) the much more rapid growth 

 of the dorsal region of the body than the ventral, preventing 

 an open coiling such as would permit of a simple assumption 

 of dextral coiling by enclosing the sinistral portion as in the 

 anastrophic apex. 



