35 



Tolayiram Par. — Accordingly on May 2nd we left Tuticorin at 6-30 a.m. and 

 proceeded to the south end of the Tolayiram Par, about 8 miles to the east of Hare 

 island. There we commenced the examination, the day's work extending over the 

 southern half of the bank, with traverses extending some distance beyond the charted 

 margin. This bank, which yielded fisheries in 1784, 1787, 1S07, 1810, 1822, 1830, 

 1S89 and 1890, has generally been considered one of the most favourable for rearing 

 oysters to maturity, and to be fully the equal of any other bank in respect to the 

 number of spat falls reported upon it during the past half century. 



It possesses by far the largest area of any productive Indian bank, its charted 

 outline being 7 miles long with a width varying from one mile to two miles. The 

 depth varies from 8 to 11 fathoms. Our examination showed the bank to consist of 

 a somewhat uneven, but not rugged, rocky framework rendered level by the accumula- 

 tion of sand in the depressions. Here and there the rock shows bare save for a thin 

 veil of sand, but the greater part is covered by sand varying from 1 and 2 inches to 

 6 inches and a foot in depth. 



The sandy bottom appears to the divers as broken up by a multitude of rocky 

 outcrops usually of limited extent and from this circumstance we may infer the origin 

 and propriety of the name " Tolayiram," literally " nine hundred ". 



The surface of the bank shows considerable local diversity — both physical and 

 faunistic. In some places a rocky surface sprinkled lightly with sand bears loose 

 blocks of calerete (recently formed rock) of varying size ; elsewhere fragments of 

 Madrepore coral branches, corroded and water-worn, lie loose, here sparsely scattered, 

 there abundant. In other places deep sand, bare of any life, largely preponderates. 

 Variation in every proportion is represented. 



The sand is altogether different from that on the Ceylon side. Instead of being 

 clean large-grained quartz grit, as there, the sand of the Tolayiram par is fine in 

 grain, the angles well rounded ; chemically it is composed principally of calcium 

 carbonate — comminuted shell fragments in the main. 



In colour it is yellowish brown and there is always associated with it a certain, 

 though variable, amount of mud particles, which rise with every movement upon the 

 bottom — the scramble of the divers, the under-tow of strong currents. 



The majority of the diving descents made upon the bank proper showed the 

 greater part of the area examined to be thickly covered with young oysters from one 

 month to six months old, those of three to four months of age preponderating. The 

 sizes varied from 10x I0|x3| millimetres to 24x22x8^ millimetres. The weight 

 of 100 individuals of average size was 99 - 65 grammes. 



The general facies of the bank approximates closely to that of the Ceylon Periya 

 par — a bank noted for the frequence of spat falls upon it ; both are of great extent 

 and of diversified character and both lie all but out of sight of land towards the edge 

 of soundings. Great quantities of young oysters were found on the Ceylon bank 

 named in March last, practically of the same age as those on the Tolayiram par, but 

 on the whole the abundance was distinctly less on the latter bank, while the sand 

 leaves less extent of rock exposed. 



Considerable destruction of the young oysters was apparent, and large numbers 

 of empty shells were found. Of the latter a small proportion, 1 in 14, bore evidence 

 in the presence of circularly bored holes, to destruction by small carnivorous 

 gastropod molluscs (belonging to the genera Purpura, Nassa and Sistrum) termed 

 TJri by the divers. The great majority, however, furnished no indication to show 

 by what agency death had been caused. Consideration of what the chief harmful 

 factor is and how it acts will be dealt with when we deal with the conclusions. 



Characteristic organisms are few in number ; sponges predominate, the black 

 crests of Spongionella nigra being frequent wherever the sand thins away. The pink 

 Petrosia testudinaria is also common, its truncate massive pile increasing the resem- 

 blance to a miniature volcano by possessing a crater-shaped excavation upon the 

 summit. Other massive but less conspicuous species are equally abundant, and in 

 some cases, I found the rapid growth of these sponges entailing the destruction of 

 many young oysters, enwrapping and smothering them, as evidenced by the empty 

 shells embedded in the sponge mass. Axinella donnani is occasionally met with. 



