No. 432.] STUDIES OF GASTROPODA. 929 
pleurotomoid shells to the perfectly flattened or even slightly 
sunken spire of certain species of Conus. In this latter genus 
it is perceptible that even in the most flattened species the 
young whorls form an elevated spire, which varies in intensity 
of slope in different individuals. The flattened or sunken 
condition appears only in the later stages. 
A type of modification of the whorl, which at least in appear- 
ance belongs here, is due to the formation of a notch in the 


Fic. 9. — Mel long Ant ture individual, showing 
growth and the spines. Slightly reduced. 
posterior margin of the aperture of the shell, where the body 
whorl joins the preceding one. This feature has so far been 
found only in the old-age stage of the individual, or in the 
adult or even earlier stages of phylogerontic types, t.e., such 
as belong to a declining group of gastropods. This posterior 
notch may cause a transgression of the final portion of the last 
‘whorl on the spire, thus covering up a portion of the preced- 
ing whorls. This is generally accompanied by a resorption of 
previously formed spines or other ornamentation which would 
