Xo. 490] ORTHOGENETIC VARIATION 



633 



primitive rounded and rihless wliorl in tlie presence (»f compound 

 spirals. This is the condition of mlwh J- iih/iir ina.n' m ii m and 



spiral which oripl.alK nlarke<l dJann-„]alion of th.' .hell 'kI- 

 These spines at iirst small, increase in si/e prou-ressivelv np lo a 

 certain point. They are simple Irianuular emaro-inations of the 

 outer lip and often are ahrnptly abandonee 1, so that they remain 

 open forward, though in other cases ilu>y are closed in front show- 

 ing a more progressive abandonment of the spine. This diminu- 

 tion of the spine-forming emargination, is generally more i-aj)id 

 than its development. This condition of newly added spines 

 following in the la.st whorl upon a smoothly rounded or slightly 

 keeled, non-tuberculate whorl is characteristic of I'lih/iir Iritonis 

 (Fig. 7), F. pilosnm, and others where a fraction of one wliorl to 

 several whorls without tubercles or spines separaic ilic piiniiti\t> 

 tuberculate, from the la.st spinose whorls (Fig. 7). The sinic is 



of the modern faniia (Fig. m. Finally in ilic iik.m -pcciali/cd 

 types, such as Fiihfiir rarini. rlicrdii.s, v\r.. and the accrlcrau'd 



back to such an e.\tcnt that the non-spinose stai^vs have been 

 dropped out. This telescoping has <!;one so far as to result in 

 partial overlapjnnir of the sj)inous and tul)erciilo>.> stages, as a 



All stages of this telescoping can readily })v olvserved in large col- 

 lections of the recent species of I'ngilina cited. ^ 



apfH-eciated. That it cnt^ out ancestral Mage, and shortens the 

 ontogeny by thi. elimination is evident, as is also the resulting 



such an ..xerhu.nini' of cliara<'ier. dcMnn. their indix idnalitv to a 



:in. .<iicli 

 lubcn'lc^ 



