fate Memoirs of the Indian Museum. IMOLANE 
beds in 2} to 44 fathoms where they are subject to the influence of rough seas and 
muddy water during the greater part of the year. They are distinctly stunted in 
general appearance and a proportion have the apex so greatly abraded as to be 
almost flat in the apical region. The apical angle of those living in depths of 2} 
fathoms averages 104 64° as against 102°52° for those in 44 fathoms. The extremes 
however range between 85° and 134°, between which perfect gradation is always to 
be seen in every batch of shells (Plate X, fig. 5). 
This great range in the angular index of the spire is due largely to the fact that 
60° 70° 80° 90° 100° - 110° 20% 130° 140° 
Tuticorin Race 
Tanjore Race 
Atlakarai Race 
Coromandel 
North Vedalai Race 
60° 70° 80° 90° 100° 110° | 120° 130° 140, 
Fic. 1.—Diagram showing by smoothed curves the respective ranges of the apical angle in three 
local races of T. pirum acuta, compared with three of T. pirum obtusa. 
this obtusa race marches with a corresponding border race of variety acuta, living 
south-eastwards, off Pillaimadam and North Vedalai, villages a few miles west of 
Pamban Pass. The commingling and overlapping of the two varieties that ensues is 
clearly seen upon reference to the apical angle chart given as text-fig. I. 
(b) The Coromandel race is found along the length of the Coromandel Coast, 
from Point Calimere to some distance northward of Madras. It is closely akin to the 
Tirupalagudi race, but is larger in average size, usually less stunted in apical develop- 
ment and in large specimens often exhibits a strong and vigorous development of 
