28 
The Chank-beds.—T hese fall into two categories (a) 
fine sands admixed with a certain amount of mud and 
known as ferals (Sq) * in contradistinction to pars, the 
rocky banks where pearl oysters live, and (6) chanku 
nilam or chank places--sands more or less mixed with 
dead madrepore branches (chad/7) and other par detritus 
adjacent to the margins of the pars or pearl banks. Up 
to the as neither survey nor tabulation of these 
chank-beds has been made—an investigation shortly to 
be undertaken. The principal are of course known and 
their positions have been shown tentatively in the sketch 
plans which accompany my feport to the Government 
of Madras on the Indian Pearl Fisheries in the Gulf of 
Mannar, (Government Press, Madras, 1905) but no 
detailed work has been attempted, and the boundaries 
given are certain to be largely amended when we have 
more exact knowledge. We have yet to learn the 
relative fishing value of the different beds and -are 
ignorant how far these are stable or variable from year to 
year. 
The principal food of the chank consists of various 
tubicolous polychat worms, chiefly small Terebellids, 
Eunicids and the like. A _ piral indeed connotes the 
presence of vast multitudes of these worms; it may be 
defined as a stretch of fine sand probably with a definite 
admixture of mud, supporting a profuse polychet fauna 
living in arenaceous tubes, on which the chanks prey. 
This constitutes a characteristic chank-polychet forma- 
tion widely spread between the § and to fathom lines off 
the Tinnevelly coast. It is noteworthy that in and around 
the pearl banks on the opposite Ceylon coast few chank- 
beds are found and chanks are not numerous except in 
a few restricted areas. In this connection we have to 
note that the Ceylon sands on the Pearl Fishery coast 
between the 5 and ro fathom lines consist of coarser sand 
grains than those of the Tinnevelly shallow water plateau 
and, unlike the latter, are generally very clean and almost 
free from admixture with mud. 
The principal piral ground lying off Tuticorin is 
sub-divided into a number of separate pirals actually 
* This name appears to be very ancient in origin ; its aerivation is unknown 
and the word does not appear in any Tamil dictionary I have consulted. 
