110 Memoirs of the Indian Museum. [VoL.-VI, | 
mentioned. This, together with the freedom from parasitic or symbiotic growths, 
shows that this race flourishes under very favourable conditions. Its principal and 
most favourable habitat is the wide stretches of sand interspersed between the rocky 
pearl banks off the Tinnevelly coast. Here tubicolous polychaets abound and these 
form the favourite food of the chank. Shells found upon or round the edges of the 
rocky banks in shallow water are less well-grown and often have symbiotic organisms 
upon them, chiefly corals, polyzoa, and algae. The columellar plicae in this race are 
moderate in size, very seldom markedly prominent and scarcely ever swollen or stout 
except in individuals living close to the littoral. 
Sinistral forms are unknown on the Tuticorin banks so far as my information 
extends. : : 
(©) The Kilakarai vace.—This race inhabits the shallow water (2 to 4 fathoms) 
lying between the southern shore of Ramnad district from Valinukam Point to Pamban 
Pass, and the chain of coral islands lying parallel to this coast. In general outward 
appearance these shells resemble closely the Tuticorin race; the apical angle is much 
the same, ranging between 62° and 89°, with a mean of 77:9° (Plate X, fig. 2—upper 
7 shells). The chief difference is that the resting phase appears to occur much more 
frequently and in these not only does the lip become thickened, but the columellar 
plicae frequently attain an abnormal stoutness and prominence, while some little dis- 
tance from the lip a low blister-like swelling, approximately 3 or I inch long by + 
inch wide, is present. The extreme thickening of the sides of the oral aperture which 
takes place in the resting phase, constricts the opening considerably and distinguishes 
these shells markedly from the more regularly grown shells from Tuticorin, where a 
resting stage is comparatively infrequent till considerable age (size) be attained. 
The explanation appears to be that in the deep water beds off Tuticorin growth 
proceeds uninterruptedly the whole year round, owing to the protection afforded by 
a deep water habitat from any interruption in feeding or periodical shortage of food 
due to bad weather conditions; hence in the Tuticorin shells the resting phase seldom 
occurs until the individual is far advanced in life. On the Kilakarai coast, the 
shallow water habitat of the local race exposes them to much disturbance during 
the prevalence of the south-west monsoon; this entails difficult conditions of life 
and begets a condition where the forces of the mollusc are necessarily concentrated 
upon thickening its shell at the mouth. As a consequence a transverse section 
of a Kilakarai chank of this description shows an alternate series of thick and 
thin places in the walls of the whorls; this is a peculiarity which renders shells of 
this race of inferior value for bangle making although the shell substance is hard and 
of good colour. These shells are largely employed as blowing conchs. 
(c) The Rameswaram race. —The individuals of this race grow to a smaller average 
size than either races (a) and (b), but as this average size is admirably adapted to pro- 
vide bangles of diameter exactly suited to the requirements of Bengali ladies, and as 
they suffer much less from the defect of irregular growth due to the frequent occur- 
rence of rest phases, these shells are actually more highly prized by bangle-makers 
than the larger shells of the Kilakarai race, Shell bangle-makers also state that the 
