14 MARCH NELL A. 



Persicula, those volutiform species having a depressed or sunken 

 spire. 



Swainson, in 1840, founded a classification upon slight differ- 

 ences in the form of the species ; extremely unsatisfactory because 

 the change of form in the series is gradual. His genera are 

 Volutella, Perxicula, Gibber ula and Glabella. 



In 1844, Hinds divided the species into two groups : Phseno- 

 spira, with elevated spire; Cryptospira, with hidden spire. The 

 first corresponds with Marginella as restricted by Schumacher, 

 the second with that author's Persicula. H. and A. Adams, 

 however, have adopted Cryptospira as a subgenus of Marginella, 

 with nearly obsolete spire, and last whorl gibbous posteriorly ; 

 following it, they place the genus Persicula, with depressed 

 spire. 



Petit, in 1851, divided Marginella into three sections : 



1 . With spire more or less elevated. 



2. With spire depressed or hidden, sometimes umbilicated. 



3. Columbelliform species, connecting with the genus Erato. 



Gray, in 1857, admitted three genera: 1. Porcellana (= Mar- 

 ginella) \ 2. Closia, for M. sarda, and not differing essentially 

 from 3, Persicula. 



Messrs. H. and A. Adams, in their " Genera of Recent Mol- 

 lusca," admit three genera : 



Marginella, with the subgenera Glabella, Prunum, Volutella, 

 and Cryptospira. 



Persicula, with the subgenus Gibberula. 



Volvaria, with the subgenus Volvarina. 



J. H. Redfield, in 1810, writes: "As to the numerous 

 subgenera which have been proposed for species of this genus, 

 they seem to me to be neither useful nor well grounded. In a 

 series of two or three hundred species it is easy to select a few 

 salient forms for subgeneric t}^pes, but much less easy to allot 

 all the intermediate species to their proper places under such 

 types. All the proposed subgenera are founded on the greater 

 or less prominence of the spire, and on the degree of the 

 thickening or reflection of the outer lip. A very slight difference 

 of the plane of development is aty that is involved in the former 

 character, and.all students of the great family Helicidse under- 

 stand well how little generic value attaches to either character. 



