No. 432.] STUDIES OF GASTROPODA. 935 
Species under consideration belongs. Thus in an ancestor of 
M. palma-rose we might expect that the principal spine on the 
last formed varix of the adult shell would have the characters 
of this same spine in an earlier varix in pa/ma-ros@ or those of 
a more anterior spine in the adult varix of that species. Such 
correspondence of characters in localized areas (e.g., a single 
varix), with the changes characteristic of the life history of the 
group, has been called by Jackson the formation of localized 
234 nE 
Bee, ag: 
fu Kits 
An LIT Ve r 123 4 
7273 3 92 
423 ZO 

y 8 4 rot 
Fic. ro. — Dia of the varices of Murex brevifrons Lam., from the West Indies. 
last or most recent varix, Z the earliest recognizable one. The corresponding spines oe 
numbered alike. The dotted line indi hat th ining p 

Stages in development, and he has found this phenomenon in 
a great many types of animals and plants.! 
One of the commonest types of varix is that due to accentua- 
tion of normal ribs. Even in the spinous Murexes the bases of 
the spines are merged in such an accentuated rib, which recurs 
with greater or less frequency, though with regular periodicity, 
in the various species. This accentuated rib, whether spinous 
or not, appears to mark the periodic culmination of constructive 
vitality, after the expenditure of which a rest is necessary 
before building again commences. 
The varices of Harpa are due to a periodic reflection of a 
smooth lip, which has the appearance of a margin rolled back. 
1 Jackson, R. T. Localized Stages in Development in Plants and Animals, 
Mem. Boston Soc. Nat. Hist., vol. v, No. 4. 
