STUkAbt CEYLON MARINE BIOLOGICAL REPORTS. Part VI.— January, 1912. Nos. 20 to 22. REPORT ON CERTAIN SCIENTIFIC WORK DONE ON THE CEYLON PEARL BANKS DURING THE YEAR 191 L With three Plates and three Charts. CONDUCTED BY THE CEYLON COMPANY OF PEARL FISHERS, LIMITED. BY T. Southwell, A.R.C.Sc. (Lond.), F.L.S., F.Z.S., Deputy Director of Fisheries for Bengal, Late Scientific Adviser to the Ceylon Company of Pearl Fishers, Limited, and Inspector of Pearl Banks, AND Lieutenant J. C. Keb.vHam, R.N.R., Superintendent of Fisheries. \^. Qt o 1 0 m b 0 : PRINTED BY H. C. COTTLE. GOVERNMENT PRINTER, CEYLON. To be obtained at tlie Government Record Office, Colombo, Ceylon ; or from the Ceylon Company of Pearl Fishers, Limited, U, Cornhill, London, E.C., iirice Rs. 2, or 2s. 8d. 1912. . o-^ Reports from the Ceylon Marine Biological Laboratory. Part VI.] Nos. 20 to 22. [Vol. I. SUMMARY OF CONTENTS. Introduction. By T. SouthweU, A.R.C.Sc. (Lend.), F.L.S., F.Z.S. No. 20.— Currents on the Ceylon Pearl Banks, Superficial and Deep. By T. Southwell, A.R.C.Sc. (Lon^. F.L.S., F.Z.S. , and Lieut. J. C. Kerkham, R.N.R. No. 21. — Nautical Notes and Observations. By Lieut. J. C. Kerkham, R.N.R. No. 22. — A Description of Ten New Species of Cestode Parasites from Marine Fishes of Ceylon, with Notes on Seven other Species from the same Region. By T. Southwell, A.R.C.Sc. (Lond.), F.L.S., F.Z.S. With three Plates and three Charts. INTRODUCTION. 1. — History of the Laboeatorv. With the publicatiou of tlus Report (Part VI.) the Ceylon Marine Biological Laboratory ceases to exist. In 1902 Professor Herdman was deputed by the Royal Society, on behalf of the Colonial Government, to investigate the various problems relating to the pearl banks, and especially the reason of the erratic nature of the fisheries. His five voluminous Reports are well known. The Reports from this Laboratory were merely intended to supplement Herdman's Reports. After Professor Herdman had finished his investigations in Ceylon, Mi'. Hornell, wlio had acted as Assistant to Professor Herdman during his stay in Ceylon, was left to continue tlie work on the spot. The Ceylon Marine Biological Laboratory was thus founded. Its fiist headquarters were at Galle, but were subsequently changed to Colombo, although the great bulk of the work has been done out at sea, on board the barque " Rangasamee Porawee." In 1903 Mr. Hornell was appointed Marine Biologist to the Ceylon Government ; dming his appointment the first two parts of the Reports from this Laboratory were published. In 1905 the pearl banks were leased out to the Ceylon Company of Pearl Fishers. Limited : Mi-. Hornell left tlie service of Government and took up duties as Manager of this Company. The Ceylon Marine Biological Laboratory thus passed from the hands of Government and became controlled and carried on entirely by the Company. In 1906 I came out to Ceylon as the Scientific Assistant to the Company. Earh^ in 1908 Mr. Hornell left the service of the Company, and I assumed full executive duties. Later in the year Lieutenant J. C. Kerklxam, R.N.R., was appointed Superintendent of Fisheries, and the scientific work devolved on me. TJiis arrangement continued up to the end of 1911, and it was dming this period that Parts III., IV., v., and VI. Reports were published. It will be noted tiiat Parts I. and II. (which arc .57-11 ii CEYLON MARINE BIOLOGICAL REPORTS. nov.- out of print) were published whilst the banks were under the control of Government. All the succeeding Reports represent a mere fraction of the work done by the Company. The Laboratory is being closed on account of the fact that the leasing of tlie banks by the Company has not proved a commercial success. I assume duties as Deputy Director of Fisheries for Bengal in December, 1911. 2. — Causes which led to the Failttbe. It is impossible to give more than a brief outline of a few of the causes whicli led to the failure Some of the factors are dealt with in Parts IV. and V. of the preceding Reports. The uncertain nature of the fisheries has been fully recognized for many centuries. Periods of barrenness have always succeeded years of plenty, and the cause was never discovered. Steuart, whose writings contain shrewd observations mixed with spicy romance, remarked in 1843 that the intermittency of the fisheries was the act of God, and beyond the control of man. The investigations conducted by Professor Herdman and by the Company had for their object, amongst other things, the elucidation of this problem. How far the investigations have been successful will be gathered from tUe Reports. As we have seen, the banks were leased out in 1905, and two successful fisheries resulted (1906 and 1907). Since then no fisheries have been held, and at the present time the banks are absolutely barren. Even when spat is found, it will be four years before it can be fished, excluding the event of its bemg lost in the meantime througli a variety of causes. The Company were granted the lease of the banks for a period of twenty years, and were boxmd by the agreement to carry out the recommendations which had already been made by Professor Herdman. The yearly rental to be paid was £20,000, and a further smaller sum had to be expended in general scientific work. The working expenses were, of course, additional. As the average profit on a normal fishery is about £60,000, it follows that in order to make the enterprise successful a good fishery must take place within every three years. The history of the banks abound with instances in which there are blanks of from four to fifty years, but in this connection it is to be noted that up to six years ago only certain paars, such as the Cheval and the Muttuvaratu, were ever inspected. Subsequent events have shown the high probability of oysters having occurred in times past at other places close by these paars, as the entire plateau is potential paar ground. These question- able blank years undoubtedly exaggerate the jjeriods of time when oysters were really absent. In view of these facts the rental paid has been excessive, as liistory has shown. For the continuity of fisheries the isolation and protection of breeding stocks is essential. It lias often been pointed out that even after a most thorough fishery there are bound to remain a few scattered oysters which escape the vigilance of the divers. This is indeed so , but it has to be remembered that the Ceylon pearl oysters have the sexes separate. They depend for their continuity on their seminal products being wafted together by the movements of the water. Thus , although after a fishery thousands of oj'sters are left scattered about here and there, it by no means follows that their seminal products come together. A distance of even one yard 7nay be fatal. Thus, if the best results are to be obtained, the necessity of leaving and protecting, say, ten compact beds of old oysters of about one acre in extent becomes obvious. During normal fisheries anything from 40 to 80 million oysters may be fished, and the number of oysters required to leave such compact and scattered beds would not be more than 1 to 2 million — an insignificant fraction of the whole. Since these facts were discovered there have been no oysters on the banks, and thus the observation has as yet had no practical fruition. It was to protect such beds as these, if found, that the Company purchased two years ago, at a cost of £3,500, wire netting sufficient to protect an aggregate of one-sixth square mile of oysters. As the pearl banks cover over 700 square miles, and as the cost of netting is prohibitive, to say nothing of the impossibility of dealing on a large scale with netting, it is clear that it could not be used very extensively, and it was never proposed to do more than protect breeding stocks to the extent indicated. Unfortmiately the opportunity has never occurred. INTRODUCTION. ii The wire netting has been immersed in sea water and its durability tested. It was found to keep intact and effective for a proved period of eighteen months, and thus wire netting would be suitable for protecting spat for this period, after which time protection would not be so necessary. The principal cause of the failure, however, has been the non-occurrence of a spatfall during the last few years. As no oysters were present on our own banks, it was obvious that if a spatfall did occur it would have to be derived from elsewhere. It has long been beUeved that young oysters (larvae) travel over to our banks from Southern India, where a few scattered and unproductive oyster beds occur. The drift bottle experiment described in this Report proves that that is not only quite possible, but that it certainly- does happen at times. Blank years on our own banks are due prmcipally to one of two causes, either to the absence of oysters on the Tuticorin banks, or to tlie failure or sluggishness of the local south-west monsoon current during the critical breeding time, which results in. the larvse failing to reach tlie plateau, and, dropping into the abyss, being lost for ever. These facts, however, do not explain why it is that when once the banks have oysters on them they should not be more or less independent of exotic spat, but maintain and develop their own. The reason is simple, and is to be found in the rapaciousness of man, whose avarice kills the goose that lays the golden egg, by omitting to leave breeding stocks ; also to voracious fish, to whom a bed of oysters is a feeding ground, to be deserted for pastures new only when the supply is exhausted. So thoroughly have the banks been devastated that during the last two and a half years less than half a dozen "shell fish " (molluscs) have been obtamed, in spite of the efforts of divers and the use of the trawl and dredge. Thus it is evident that other, and probably all, "shell fish " suffer equally with the pearl oyster, and it is only on account of the commercial importance of the latter that the loss is noted. Now that the banks are depleted of all molluscs, fish of all species are remarkably scanty; but one cannot doubt that, as in past ages, when the banks do recover the fish will return. A fuller and more detailed account of the ravages caused by fish will be found in Part IV. We thus come to agree with Steuart that in some respects the continuity of fisheries is dependent on natural events which are beyond the control of man. But whilst this is so, we can almost escape this catastrophe, and in any case extensively mitigate it, by reserving breeding stocks of old oysters in the way indicated ; and, although even thus one could not hope to emulate the luxuriant bounty of Nature, such breeding stocks would at least make the enterprise a successful one commercially. The importance and significance of trawling, dredging, and transplanting were fully dealt with in Part V. Report, and need not be further considered here. In the present Report the subject of currents is extensively dealt with. The importance of the surface currents prevalent during the spattmg season, and their relation to the natural distribution of oyster larvae, cannot be exaggerated. Assuming oysters are present on the Tuticorin side, a spatfall on our own banks is certain if the south-west monsoon continues strong at the critical breeding time. If the monsoon is weak or erratic, then the larvae either di-ift through Paumben Pass, or drop into the abyss on their way to the pearl banks, depending, of coiu'se, on the topographical position of the larva? wlien the fluctuations of the monsoon begin. It is very noteworthy that the facts which have been obtained fully and naturally explain why our banks usually retam their own spat as well as receive exotic deposits, whilst the Tuticorin banks and those banks still under Government control are not only destined to lose their own spat, but are situated in such a way that exotic falls of spat thereon are almost physically impossible. These facts are amply borne out in the history of the areas concerned. Considerable misapprehension has existed during past years m relation to currents in genera! over the banks. If a bed of oysters has disappeared, the cause has been attributed to currents, no other explanation being obvious. Not only so, but the distinction between a top and a bottom current has not been appreciated. A strong drift may be present on the surface of the water, which is not felt at tlie bottom. Our experience, extending as it does over five years, has furnished no indication what - ever of a bottom current, even though we have had access to the diving dress as well as the information afforded by skin divers. We are of opinion that bottom currents do not exist, and that the loss of beds of oysters in past years was probably never due to this cause, nor to silting over by sand. IV CEYLON MARINE BIOLOGICAL REPORTS. Ha\"ing thus outlined in merest detail soiuo of the linuiustances whicli liave led to the failure of the enterprise, it would be well to now consider what ought, in our opinion, to be done in the future. 'A. —The desirability of forming a Government Marine Department. The pearl fisheries represent the olde.st, and probably the largest, source of revenue to the Govern- ment that is, and its extensive nature fully warrants the attempt being made to make the banks as lucrative and successful as possible. What is required in Ceylon is a Government Marine Department, with a special staff of two or three suitably trained men. whose 07ily duty would be to fully investigate and enhance the marine resources of the Island. The primary work would bo a continuation of the scientific research initiated on the pearl banks. During the south-west monsoon, when operations are impossible on the ]3earl banks, there would be the investigation of tlie Placuna fisheries on the sheltered side at Tamblegani, or the investigation of the fresh-water fisheries. In addition to these, chanks are fairly plentiful on muddy gromid, and this industry could be made profitable. Finally, fish trawling investi- gations could be carried on, and this industry placed on a scientific basis. It would be impossible to do this work without a special staff. A Marine Department could be run for from £2,000 to £3,00(J per aanum successfully, and if a single pearl fishery resulted once in from twenty to thirty years, the Department woidd liave paid for itself, to say nothing of the other industries. Other fisheries over and above the one named would represent clear profit. One has only to turn to the Madras Presidenc3^ and many other places elsewhere, to find that even the minor marine industries are placed on a proper and lucrative footing. Ceylon is unique in this respect in possessing the finest pearl fishery in the world, and tins fact itself is sufficient reason why a special department should be estabUshed. What Peradeniya has done for agriculture in Ceylon — for tea, rubber, coconuts, &c. — can be done by a Marine Department with the pearl fishery and other marine industries. The difficulties with the fisheries here when under Government control have ahuost always been that the various officials pro tern, were merely casually deputed to reap the harvest of the sea, and had no time nor business to seek to enhance its value, or to ensure its continuity. There are instances on record, and not far remote, when by the merest chance Government conducted huge fisheries wliich might easily have been lost. We have no doubt whatever that these incidents have been numerous in the past, but there is necessarily no record to show. Instances are more numerous still ui which beds of oysters two, three, fom', and even five years old were discovered for the first time. If the inspections had been carried out with that thoroughness which so large a source of revenue warrants, these oysters would have been discovered before they were three months old. It is also equally clear that if beds have frequently been found of this age, other beds have never been found at all. The discovery of a bed of oysters two, three, four, or five years old indicates tliat the necessity of an extensive survey of the pearl bank area has not been thoroughly appreciated. No inspection is either satisfactory or adequate wliich does not every year systematically and fully cover the eniire plateau ; and so long as inspections are merely confined to a few paars, beds of oysters are bomid to be lost. Oysters or spat, when they occur, ought to be discovered at once, and watched and tended with that care which the circumstances demand. The rectangular method of inspection adopted by the Company leaves no part of the ground unexplored. It is described elsewhere. The pearl bank area is to be regarded as wholly ijotential, and not as consisting of a number of j)aars. The notoriety of the Clieval and Muttuvaratu Paars as very productive areas is merely incident on their having been more frequently examined. In fact, up to five or six years ago these were practi- cally the only areas inspected. As the recent investigators went further afield, other productive paars were discovered, and there is every reason to believe that oysters flourished tliereon occasionally from time immemorial, and were never sought for. As we have already noted, the area under lease covers over 700 square miles : there is still much potential ground not under lease. The entire area covers approxi- mately over 1,200 square miles. The thorough inspection of tliis area would fully occupy six months. It thus becomes evident that tliere is emiJloyment for two trained and expert men, and I have no doubt in my own mind that the establishment of a Marine Department would not only be a successful venture, but that in a short time it would prove to be one of the principal and most lucrative sources of IXTRODUCTION. v revenue to the Colony. Wlien the banks revert to Government, it will be pathetic if those rough, ready, and casual methods of inspection and control wliicli liave come down to us with the banks themselves, are continued. 4. — -General. The legacy left by the Company to Government consists of the information contained in tlie various private reports sent in to them, of the four Marine Biological Reports, of a chart of the Cheval Paar drawn up from a recent survey, and of a large new nautical and biological chart of the entire plateau under lease, the latter having taken practically five j'ears to prepare. In addition to these, the positions of various trigonometrical and other stations have been verified and the structures repaired. Beacons have been erected on various reefs, and although these are not permanent structures, tliey will survive for many years. Hatchery and nursery tanks are fitted up complete at Marichchukaddi. A survey of Dutch Bay has been made and a chart pubUshed, and this information has conclusively shown the unsuitabUity of this place as a seaboard nm'sery. The general experimental work carried on by the Company at enormous expense has been of so extensive a nature, and so conclusive in its results, that it need not be repeated. The faunistic and other specimens collected during five years, including the tow net catches extending over four years, have been sent to the Government Museum, Colombo. These are some of the benefits other than j)urely pecuniary ones which have been derived by Government from the Company. I take the Uberty of referring here to the introduction of X-ray photography to oyster culture (?) in Ceylon, as considerable misunderstanding exists on this point. Some years ago an X-ray plant was laid down by Mr. John I. Solomon in the vicinity of the pearl banks. The object was to X-ray oysters, to separate those containing pearls, and to put these back again into the sea for the pearls to grow. It is to be remembered that the Companj' only fish old oysters. It would seem a far cheaper way (even if less dignified) to proceed in the usual way in the determination of the pearl yield rather than to X-ray the oysters. If the oysters have pearls, they will not grow appreciably bigger during the short span of life which remains to the oyster. If pearls are not present, then these expensive operations are wasted. Even if young oysters are being dealt with, the X-rays will not manufacture or initiate pearl formation, and thus the operations appear useless and extravagant. When one considers that young oysters, when they do occur, are found in the quantity of at least half a million per acre, and that the maximum that can be X-rayed per minute is about sixty, the impossibility of the iiroceeding as a commercial undertaking is evident ; and even if the oysters could all be X-rayed in one second, there seems to be no object in attempting it. In Japan an extensive and successful industry is carried on m pearl culture. Small leaden images of the Buddha and other nuclei are inserted between the mantle and the shell, and these, setting u]) local irritation, in course of time become partially covered with pearly matter. After they have grown sufficiently large they are removed, and the basal part of this concretion (wliich has grown to the shell) is carved out of the shell. These artificial pearls are always used for mounting, tlie basal face being hidden in the moimt. Since probably not '01 per cent, of the larvaa inhabiting the tissues of the pearl oyster ever become the nuclei of pearls, it would appear likely that future science will concentrate on so treating the oysters that a large percentage of these larva? will form pearls, as it appears very probable that only such larvae which for some unaccountable reason die in the tissues, and thus set up local y-ritation, form pearls. If this is found possible in future years, pearl fishing will be revolutionized. Consequent on the entire absence of oysters on the Company's banks, numerous suggestions have been received from time to time advising the stocking of the banks with oysters from elsewhere — Mergui. Torres Straits, Persian Gulf, &c. Xeedless to add, all these suggestions have been passed by. It has taken ten j^ears to collect what little we know of our own oyster. Apart from the expense and probable impossibility of successfully transplanting these exotic oj'sters over long distances to our banks, we have no reason to believe it would occupy a less time, if transplanting was successful, to acquire the knowledge concerning them that we possess about the pearl oyster. Motlier-of-pearl oysters have totally different v\ CEYLON MARINE BIOLOGICAL REPORTS. liabits, and if success is doubtful with them in their own natural surroundings, it would obviously be more so here. The Mergui oyster lives in 20 fathoms on a muddy bottom, over which a 7-knot current rtows. and where there is a rise and fall of 15 feet of water. Our banks are rocky, covered with only an average of 8 fathoms, and bottom currents are absent. The futility of transplanting such oysters is obvious. The Ceylon pearl banks do not require supplementuig with exotic oysters. Given a spatfall, only thorough inspection, care, and normal foresight in isolating breeding stocks, &c., are required to make the banks perennially productive. A spatfall is almost certain to take place at an early date, and to our successors will be given the opportunity of reajiing where we have sown. In conclusion, I beg to express my indebtedness to the Ceylon Government for kindly publishing these resiilts ; my thanks are also due to my wife, for correcting proofs and for really serious and extensive help in many other ways. r. ^, ,^ T. SOUTHWELL. At Sea, Cheval Paar, Ceylon. November 18, 1911. CURRENTS. 231 No. 20. CUREENTS ON THE CEYLON PEAEL BANKS, SUPEEFICIAL AND DEEP. By T. SOUTHWELL, A.R.C.Sc. (Lond.), F.L.S., F.Z.S., and Lieut. J. C. KERKHAM, R.N.R. With three GJmrts. The interest attaching to currents on the pearl banks Ues almost wholly in the relation they bear to the oyster, for it is commonly believed that beds of spat or adult oysters have from time to time been entirely swept away by the agency of bottom currents. It is important, in the first place, to note that the oyster is stationary, and almost defenceless against the vast majority of its natural enemies. Pish of various species devour them omnivorously. Subtle and fatal diseases attack them. A variety of other animals compete with them for food, and often grow on their shells, as if to purposely arrest and accommodate such food as the gentle undulations of the bottom layer of water may bring near by. The outstanding character of the oyster (Margaritifera vulgaris) is its sedentary habits, and the power it possesses of holding on to rock and other solid objects in such a way as to remain securely attached. This condition is essential to the oyster's welfare, and so strong and powerful is this attach- ment that it is only with difficulty that divers are able during fishery times to dislodge them from their anchorage. The attachment is made by means of a beard or byssus, similar to that occurring in the ordinaiy Enghsh mussel {Mytilus edulis). A very considerable percentage of oysters lose their byssus in being pulled away from their attachment. This structure can, however, be replaced in a very short time, and if necessary many times in succession. In deaUng with currents on the Ceylon pearl banks, it is essential, in the first place, to carefully distinguish between surface and bottom currents, for they bear different relations to the oyster. There- fore, in order to understand these relationships better, we will deal with each separately. I. — SUEFACE CHREENTS DUBING THE NOETH-EAST MoNSOON. Investigations of the surface currents have been carried on intermittently during the last four years, but only during the north-east monsoon. The observations on the south-west monsoon have only been carried out during two seasons, viz., 1908 and 1910. The results during the latter monsoon were in every sense satisfactory. The percentage returns were high (51 "5 per cent.), and the results of each year's work were similar. In 1910 alone 565 bottles were released at different stations during the south-west monsoon, of which 291 were returned ; whilst in 1908 only 80 bottles were released, and 47 returned. The results from many bottles hberated during the north-east monsoons of the last four years have had to be discarded, owing to the fact that the management of these drift bottles changed hands, and the results of the first two years' work were useless, as the necessary data was not obtainable. This paper, therefore, embodies the result of two years' work during each monsoon, viz., those of 1908 and 1909 during the north-east monsoon, and those of 1908 and 1910 during the south-west monsoon. Full statistics are given at the end of the j)aper. Apart from the drift bottle expesiments, our knowledge and experience has been further extensively supplemented by the observations made by commanders of coasting vessels, some of whom have had many years' experience. '2:\-2 CEYLON .MURINE BIOLOGICAL REPORTS. Tlieso investigations Mere oairiod out on tlio west side of tlie Island (between Galle and Adam's Bridge), where, of course, the pearl banks ho, and also on the Indian side, and in the Gulf of Mannar generally. It is necessary at the outset to understand tliat the pearl bank area of the Ceylon coast consists of a sliaUoM- water plateau, slielving out from the beach to about the 12-fathom hne, and then rapidly deepening to several hundred fathoms. The overfall ranges froni 1 to 18 miles from the beach. The bottom consists of alternations of sand and hmey rock, which latter is derived from decayed coral re-organized into an exceedingly hard substance by the cementing growths of NuUipore and Polyzoa. At mo?!t places the rock is only covered by less than four inches of sand, and is often quite bare. These details have been obtained as a result of continued dredging and trawling operations, combined with the extensive work of skin diving and also dress diving. Practically parallel to the shore, whicli runs approximately north and south, there is a more or less continuous, fringing, coral reef, exposed at places during low water. The rise and fall of tide is limited to a few inches only. Towards the north of the plateau the submerged continuation of Karativu Island rims in a northerly direction for about 10 miles as a narrow sandy shoal, and terminates very abruptly. Reference to the apj)ended chart will indicate the topographical relations of the mainland. To the north the pearl banks under lease he in a cul-de-sac. The only exit to the gulf is Palk's Strait, whilst Southern India forms the western boundarj'. The influence of these varied factors on the surface current will, however, be dealt with later. It is obvious that during the north-east monsoon the surface current over the entire plateau has a different trend to that existing during the south-west monsoon, so that in order to fully elucidate and miderstand the true condition of affairs we wiU deal with each monsoon sej)arately. (a) North-east Monsoon. This monsoon commences about the beginning of November and extends until about the end of May. It is the fine weather season, as the wind is from the land. During November, December, and Januaiy strong northerly winds prevail during the day, usually becoming almost easterly at or durmg the night. In February these strong winds gradually die down. During March and April dead [Trichodesmium) calms prevail about midday. An hour or more later a gentle breeze springs up from the west, and as it strengthens it veers to the north, and by nightfall is due east from the land, where it continues during the night, shifting again to the south in the morning hours and gradually dying away at daybreak. These conditions have been noted during a great number of years, and although the sequence of these daily changes of the wind is occasionally broken, they still remain a very noticeable feature about this time. During the fisheiy season the westerly afternoon wuid enables the fleet to sail ashore, whilst the early morning easterly winds waft them back again to the fishing grounds after they have disposed of their oysters. In May these rhythmic winds are almost entirely broken up, and are succeeded by cakn mornings and exceedingly squally afternoons, characterized by heavy rains ^dth hghtniag and thmider. Thi condition marks the approach of the south-west monsoon. In thus considering the currents prevalent durmg the north-east monsoon, it will be noticed from the cliart that the pearl bank area under lease hes in a cul-de-sac, where it is entirely protected by the luaiixland and the line of fringing reefs. The banks south of Tallaivillu Point are swept by an oceanic current, wliich, running north, is deflected at this point to the west and on to the Lidian coast. North of TaUaivOlu Point, however, it may be said that there are no true surface currents, except far out at sea. Wliat surface currents exist on the plateau are transient and temporary, and vary even during the day with the direction of the wind, bj- which thej' are controlled and to which they entirely owe their existence. This area hes securely under the lee of the land, and is further protected by the line of fringing reefs previously mentioned. The situation of the banks renders them immune CURRENTS. 233 from oceanic currents, and bottles liberated on this area took one of two courses. If liberated well inshore, they were di'ifted south as far as Dutch Bay by the prevaihng northerly wind. If hberated a little further west to the overfalls or beyond, they eventually drifted over towards Cape Comorin, being first blown south by the prevailing wind, and eventually they became involved in the oceanic current named, which rmis along the west Ceylon coast in a northerly direction as far north as Tallaivillu Point, and then takes a westerly direction to the Indian coast towards Tuticorin, from whence it runs south, and, roimding Cape Comorin, has been traced as far north as Cahcut. The current thus sweeping west runs out into the Indian Ocean, where it is lost, but it is exceedingly interesting to note that we have had a bottle returned from the Maldive Islands. This current, as it sweeps round Cape Comorin, still runs in a westerly direction, although owing to the configuration of the land offsets from the main current have been traced as far north as Calicut. Prom the above it will be gathered that bottles hberated along the Indian side and the Ceylon side (except on the inshore areas under lease) have usually been lost. The percentage recovered is small (16'76 per cent.), and such bottles consist entirely of (a) those liberated inshore on the areas under lease, which merely drifted south on to the beach by the prevailing north wind, these form the bulk of those returned; (6) those which were hberated further out at sea, west of the above area, which first drifted south ^v'ith the prevaihng northerly wind, and eventually becoming involved in the westerly current, drifted over to the Tuticorin side ; while (c) those which were liberated to the south became directly involved in the westerly oceanic current named and were carried up the east coast of Lrdia. As we have seen, however, the vast majority (83 '24 per cent.) were lost, being carried away into the Indian Ocean by the oceanic current. It is to be noted that during this monsoon a steady flow of water passes through the Paumbeu Pass, from the north to the south side, and has been noted by such steamers as regularly pass through. This current of water, however, passes out into the Gulf of Mannar and is never felt on the area under lease, which hes to the extreme north-east of the gulf. The pass through the Mannar Channel may be altogether neglected. Durmg tire south-west monsoon this channel becomes silted tip. With the advent of the north-east monsoon the water collecting to the north and north-east of Mannar island quickly scours out the channel, but the effect of this is only felt for a few days on the area under lease. After the channel is clear no further current is noticed. A reference to the chart wiU show how insignificant and temporary the eiiect of this channel is. Over the area under lease then, occurring as it does in such a secluded position, away and protected from all disturbing oceanic influences, the essential conditions for a calm sea (save such as is caused' by wind, and therefore temporary in character) prevail. On this section of the plateau alone 300 drift bottles have been hberated. Of these, 57, or only 19 per cent., were returned. We have in the above been referring purely to the northern head of the gulf. South of Tallaivillu Point, however, an entirely different set of conditions prevail. Here, as we have seen, a very decided current nms along the coast in a northerly direction, and in the face of the north-east monsoon. This current is known to exist throughout the entire monsoon, and is reckoned with and allowed for by local vessels. Its origin is a httle obscure, but its occurrence is beyond possible doubt. Its rate averages 0 • 3 knot per hour. It appears to rise as an offshoot from the current produced on the east side of the Island during the north-east monsoon, which, running in a general southerly direction, flows into the open sea to the south-west of Ceylon. A branch from this volume of water rounds the south end of Ceylon, and runs north along the West Ceylon coast. This current on reacliing Tallaivillu Point takes a due westerly course towards Tuticorui in South-east India. From tliere it runs south, and rounding Cape Comorin flows north along the west coast of India, and has been traced as far as AHeppe and Calicut, although the main current passes west and is lost in the Indian Ocean. This current continues througli January and February, and ceases as the strength of the monsoon dechncs in March. During April and May there is no current noticeable, and this condition continues until the south-west monsoon sets in. The explanation of these facts may be difficult, but the presence of tlie current under consideration is unquestionable, for not only have drift bottles liberated m the vicinities concerned been recovered on the Indian side and in the Maldive Islands, but, as before noted, commander.'} of vessels traversing this tract are perfectly familiar with its direction and liave helped the writers considerably. .57-11 234 CEYLON MARINE BIOLOGICAL REPORTS. It is interesting to further find tjiat Steuart in his " Notes on Ceylon " (1843) points out that "ships leaving Bombay in the height of tho north-east monsoon, to load cotton at Tuticorin, after passing Capo Coniorin find tho soutliern current so strong as to induce them to stretcli across the Gulf of Mannar, and beat up the western coast of Cej'lon until tliey can steer for their destined port, and this they accomplish against what is called in Ceylon ' a long shore wind.' " This old-time observation fully amplifies our statement of the prevalent currents, and falls in line absolutely with our own observations. To summarize, then, on the west coast of Ceylon the surface disturbance falls into two sharply defuied sets, each set being strictly limited to a particular area, as under : — (1) North of Tallaivillu Point (which comprises the pearl bank area under lease) the conditions of entire protection from oceanic currents and from the north-east monsoon exist on the insliore areas. Such disturbances as there are are purely local, varying, and intermittent, and are entirely due to the \\'ind, which is invariably from the north over the plateau. Tliis surface drift running south finds a ready exit in Portugal and Dutch Bay, and the changes taldng place in the latter backwater may in some measure be due to the presence of this surface drift. Further out at sea, and to the west of the plateau, northerly winds stiU prevail, and consequently tliere is a defuiite surface drift, which runs south for some distance. Eventually this drift joins the current running nortli (in the opposite direction) along the West Ceylon coast, and from about Tallaivillu Point rmis west. Some bottles liberated about this vicinity have been recovered on the East Indian coast. The majoritj', however, were lost. Li some cases a few rounded Cape Comorin, and were recovered on the West Indian coast as far north as CaHcut, but the main current passes west into the Indian Ocean, and the bottles were consequently lost. One alone was returned from the Maldive Islands. (2) South of Tallaivillu Point a definite current runs from the south of the Island in a northerly direction at an average rate of 0-3 knot per hour, and in the face of the north-east monsoon. This current is deflected about Tallaivillu Point, and from there takes a westerly course towards the Indian coast, and then, turning south, rounds Cape Comorin, and has been traced north along the west coast of Lidia as far as Calicut. But the main current runs west into the Indian Ocean. It is cei'tain that the secluded and sheltered position of the pearl bank area under lease as distinct from the pearl bank area still under Government control, and which latter hes south of Tallaivillu Point, owes its larger degree of productivity to the incidence of its protected position. It is also evident, a priori, that such surface disturbance as does exist there is not sufficient to affect oj'sters whose natural habitat is in from 5 to 10 fathoms of water. It might be argued that on a shallow water plateau such as exists on the west of the Island no surface current or drift could exist at all which did not affect the bottom on which the oyster lives. There are certainly movements of the water on the bottom, otherwise stagnation would result. But these movements are undulatory. They are vertical, and not horizontal. The total efiEect of the surface movements on the area imder lease with regard to the oyster is nil. They certainly are not harmful. The relative productivities of the areas (a) under lease and (h) those still under Government control has a deeper origin. But before attempting to discuss the matter further, we must first understand the nature of the surface currents during the south-west monsoon, for these currents in toto have a very real relation with the pearl oyster. II. — SuBFACE Currents during the South-west Monsoon. We have already pointed out in Part III. Report of this series that the south-west monsoon on striking Cape Comorin is deflected in such a way that it runs approximatelj' east and reaches the Ceylon coast about Tallaivillu Point, and then runs south. It will be noted that the current, therefore, runs exactly opposite to the one prevalent in the north- east monsoon, and not onty has it a definite course, but a more definite origin. This oceanic current, running as it does in its easterly course from Cape Comorin (and which has been felt as far north as Tuticorin), plays a very prominent and important part in the determination of the currents prevalent in CURRENTS. 235 the gulf, for with its fluctuations in strength the whole trend of the flow of water in the entire gulf changes. When the monsoon is ■weak this oceanic current is scarcely felt, and the south-west monsoon has full play in the gulf, where the current then runs north. When the monsoon is strong and steady, this oceanic current has an easterly course from points between Cape Coniorin and Tuticorm, and reacliing the Ceylon coast about TaUaiviUu Point, turns, and runs south. These details have been repeatedly corroborated by commanders of local coasting steamers who have had long experience. And dui-ing the south-west monsoon of 1910, 565 drift bottles were liberated at various points in order to confirm the above facts. Of these 565 bottles, 291 were returned, giving a percentage return of 51*5 per cent. In this connection it is important to note that with reference to drift bottles liberated in otlier parts of the world the usual and average percentage return is one-tliird, or 33 per cent., so that our experiment was very successful. The south-^vest monsoon usually commences in Jmie, and we started Hberating bottles at definite stations at the end of June, 1910, and continued until September. The following is a summary of the results. Drift bottles liberated off Cape Comoriu and off Colombo late in June, before the monsoon had become severe, were recovered in the vicinity of Paumben, indicating a northerly current on both sides of the gulf (viz., on the west side of Ceylon and the south-east side of Lidia). Early in July, as the monsoon freshened, bottles liberated off Cape Comorin and Tuticorin took an easterly direction, and were recovered along the Ceylon coast, from south of TaUaiviUu Point to GaUe, and even Dondra Head, including Chilaw, Negombo, and Colombo. Bottles liberated off Colombo were also recovered to the south. This result clearly indicates that the oceanic current in the fuU force of the monsoon runs east to the Ceylon coast and then turns south, foUowing the contour of the land. The average rate of this current was fomid to be 0- 5 knot per hour on its eastward course, and 1 knot when running south along the Ceylon coast. The reason for the increase in the speed of the current wiU be dealt with later. It is significant that along the Ceylon coast south of TaUaiviUu Point the current runs in the teeth of each prevailing monsoon. This current continued to flow untU nearly the end of July, during which time the south-west monsoon blew strong and steady. At the end of July the monsoon moderated and feU light, and the current was then observed to reverse and to run north again along the Ceylon coast, and also along the Indian coast from Cape Comorin to Palk's Strait. During this lull, which continued untU the middle of August, bottles liberated off ChUaw and TaUaiviUu Point on the Ceylon coast were recovered north, at the head of the gulf, in the vicinity of Paumben and Adam's Bridge. Those hberated off Cape Comorin, Tuticorin, and Manapad were also recovered at the same place. The monsoon strengthened again during the second week in August, and bottles hberated off Capo Comorin and Tuticorin were again picjked up off the Ceylon coast as far south as Dondra Head. This recurrence of the oceanic easterly current during strong south-west monsoon conditions was felt at Tuticorin. The current continued steady up to the end of August, when the monsoon again began to abate. During this third luU in the monsoon the current again took a northerly course, rumimg at a rate of 0 ■ 3 knot per hour ; and bottles liberated off Cape Comorin were agam recovered at Paumben, Delft island, near Kayts, also at Point Calimere, 70 miles north of the Paumben Pass, and even at Tranquebar, 120 miles north of the Paumben Pass, both the latter points being on the Lidian coast. The explanation of these apparently anomalous results, which admit of perfect co-ordination, is not merely interesting, it is important. As we shaU shortly see, this oceanic current produces different effects on the Ceylon coast, for, as already pointed out, on tlie banks not under lease and south of TaUaiviUu Point the oceanic current runs south when the monsoon is strong, and when weak it rmis north with the \vind ; whUst on the area under lease there is merely a surface drift dependent, as usual, on the wind. In now attempting to explain the irregularities of the oceanic current and the results relating thereto, we would draw particular attention to the charts appended, without which it wiU be difficult to foUow the text. 236 CEYLON MARINE BIOLO(}ICAL llEPORTS 'J'ho preseuce of an oceanic current from the west during the south-west rnonsoon is a well-established fact. During a weak or moderate monsoon this current never penetrates the gulf at all. It is only when strouix and continued south-west conditions prevail that the oceanic current becomes as it were pushed up into the gulf by the continued effects of strong wind and south-west sea. We have already seen that unless the monsoon is very strong there is a northerly current at the head of the gulf, particularly on the Indian side. This northerly current, aided by the -wind, finds an exit through the Paumben Pass, through which a steady current runs to the north during this monsoon. This current through the pass represents the normal flow of water consequent on the monsoon effects in the gulf. When the monsoon is not particularly strong, the oceanic current does not penetrate the gulf, and the Paumben Pass under these conditions provides a sufficient exit for the volume of water wliich is continually being blown into the gulf during the south-west conditions. Consequently the northerly current is felt on the Indian side and on the Ceylon side south of TaUaiviUu Point. We would here point out that the Mannar Channel and the passes through Adam's Bridge become silted up during tlie south-west monsoon. It will be seen that the banks imder lease are situated in such a position that they are protected from this northerly current. What " current " there is on this area is due purely to tlie wind. We, therefore, find that bottles liberated off Cape Comorin during a moderate monsoon find their way through the Paumben Pass, and have even been recovered as far north as Cape CaUmere and Tranque- bar ; whilst bottles liberated off the Ceylon coast north of TaUaiviUu Point merely drifted ashore with the wind north of the point where they were hberated. Bottles hberated south of TaUaiviUu Point also merely drifted ashore during a hght or moderate monsoon, and were recovered north of where they were libei-ated. These conditions are, of course, what one would naturaUy expect from the lie of the land. During a strong south-west monsoon, however, the currents run quite differently. Then, owing to the force of the monsoon, the oceanic current partly penetrates the gulf, and the water at the head of the gulf becomes piled up. During a strong monsoon the sea level at the head of the gulf is 9 inches above the normal. The exit through the Paumben Pass is insufficient to carry away the volume of water which coUects in the gulf. The stronger and more continued the monsoon, the further into the gulf does the oceanic current penetrate , and the larger the head or cushion of water formed there. This current is purely oceanic, and penetrating the gulf takes an api^roximately east and east-south-easterly course, and reaches the Ceylon coast south of TaUaiviUu Point. It is here joined by a volume of water, which represents an overflow from the head or cushion of water which has become jjiled up in the gulf, due to the penetration of the oceanic current. So that there are two exits for the water which becomes pUed up at the extreme north of the gulf during strong monsoon conditions. There is the Paumben Pass and the south-eastern extremity near TaUaiviUu Point, at which latter point the oceanic current turns south. The drain of water at this latter place, together with the Paumben Pass, provide exits (^vithout producing currents) for the volume of water which has coUected north of where the oceanic current has penetrated the gulf. These exits are merely escapes for the water which has accumulated above its normal level and is therefore under pressure. The rate of the oceanic current as it sweeps eastward is 0 • 5 knot per hour. South of TaUaiviUu Point, where it is joined by water which helps to drain away the " laead " of water referred to in the gulf, it obtains a speed of 1 knot per hour. Bottles hberated in the height of the monsoon off Cape Comorin and off Tuticorin were recovered at points along the Ceylon coast from TaUai^^Uu Point as far south as Dondra Head ; whilst those Hberated off the Ceylon coast south of TaUaiviUu Point were recovered south of where they were liberated, and those liberated north of TaUaiviUu Point were recovered to the north, having been merely driven ashore with the wind. When the oceanic current penetrates the gulf, it becomes evident that the northern current ceases to exist, for it is obstructed by the oceanic current. Those forces (wind and sea) which normaUy produce the northerly set are expended in pushing the oceanic current into the gulf. North of this point of CURRENTS. . 237 penetration the surface movements in the gulf are purely due to wind, which near the Lidian coast blows from the west, whilst further out at sea the wind becomes soutli-west. It is important to note that during the south-west conditions a strong westerly wind is continually blowing with some force over Southern India, and is persistently recorded at Tuticorin. The oceanic current is thus assisted considerably in its easterly course by the prevailing wind. We thus see that the surface currents during the south-west monsoon have two phases, and it will be weU to here summarize them : — (1) A hght or moderate monsoon, when the currents rim northerly towards the Paumben Pass, both along the Indian coast and along the Ceylon coast south of Tallaivillu Point (only), where the water finds an exit. (2) A phase of strong monsoon, when the oceanic current penetrates the gulf, and the water at the head of the gulf consequently becomes piled up as a cushion. The oceanic current, aided by the westerly wuid which prevails over Southern India, takes an easterly course, and eventually reaches the Ceylon coast about Tallaivillu Point. It is here joined by an overflow of water from the head of the gulf and then runs south on the Ceylon coast. This penetration of the oceanic current into the guK destroys the northerly set towards the head of the guU, for the forces which normally produce this northerly current have been expended in pushing the oceanic current north. The drift over the volume of water north of where the oceanic current penetrates is solely due to the prevailing ^inds ; whilst at Paumben Pass and Tallaivillu Point there are exits for the water therefrom, -which, being above the normal level owing to the penetration of the oceanic current, is under pressure. In the table given at the end of this paper an interesting transition between the two phases of the south-west monsoon current is shown. (Chart B.) On July 25 strong monsoon prevailed and the oceanic current ran east, as indicated on Chart A. On July 28, 20 drift bottles were liberated just off Tallaivillu Point. These travelled on the head of the water north of the penetration of the oceanic current and were blown ashore at Mannar, where 18 were recovered. This fact indicates that the water towards the head of the gulf dm-ing a strong monsoon is dead, and that the drains or outlets to this head of water at Paumben and TaUaiviUu merely relieve the pressure without producing currents. The surface movement at such a time is merely due to the wind, as was shown by the bottles going ashore at Mannar. A week later, as the lull in the monsoon continued, the head of water had had time to drain away, and a northerly set of the current was re-established. It was found that of 20 bottles liberated at the same station, 17 were recovered at Paumben. These facts are most instructive, and clearly corroborate the ideas regarding the currents during the south-west monsoon set forth in this paper. During our investigations this year we found that the monsoon went through each phase twice and then died a%\ay. We attach no importance to these numbers at all, believing as we do tliat tlie phases named alternate with each other irregularly year by year. Two things now become clear. On the pearl banks under lease, i.e., those north of Tallaivillu Point, there are no true currents during this monsoon. There is a surface drift trending to the beach on uishore areas and due to the strong prevailing \vind, but the banks are completely out of Une with, the chrection of cither phase of the surface south-west current. On the banks south of Tallaivillu Point, and stiU under Government control, the current runs south and in the teeth of the monsoon when the monsoon is strong ; whilst when the monsoon is weak or moderate the current merely becomes a surface drift, due, as on the banks under lease, to the wind, and invariably running north towards the shore. In our report to the Ceylon Government on the inspection of their banks, i.e., those south of Tallaivillu Point (Part III., " Ceylon Marine Biological Reports"), we stated that the banks under lease owed their productivity to the fact that they were protected, and that owing to the deflected current above described being furtlier acted upon by the south-west wind and sea, exotic spat drifted on to our banks, L\*iS CEYLON MARINE BIOLOGICAL REPORTS. but never or seldom reached the soutlicni paars. The statement is only partly true, but our investigations ^^•oro at that time in their infancy, and the results of further investigations have enabled us to understand the situation better, even though the factors at work are still somewhat complicated. It is to be remembered that pearl banks exist in the vicinity of Tuticorin, and it has been for a long time believed that sj)at from the oysters there drifted at times on to our own banks, i.e., those under lease. This circumstance is by no means impossible, or even at times unlikely. Vk'o must further note that oysters usually .sj)at in July and August, and that their microscopic larv£e float about on the surface of the sea for about the first five to seven days. The exact period is somewhat uncertain. The larvae are, therefore, liberated in one or other of the phases of the surface current during the south-west monsoon, and the M-hole interest attaching to surface currents hes in the distribution of these larvae, which is effected by the surface current at the time of their liberation. The entire plateau on the West Ceylon coast is potential paar ground, and other and less productive tracts occur as noted near Tuticorin. It is evidently important to know what becomes of the spat shed by oysters living on the several areas. If the spat is retained on the area where it was liberated, the bank within limits continues to be productive. If the spat drifts away, the oysters tend to eventually become extinct. On the other hand, if wcll-defuied currents exist, there is always the possibihty of banks on one area being replenished with, spat from other areas, which latter must of necessity be remotely distant. This phenomenon has been repeatedly -natnessed on the pearl banks under lease. There have been periods when on this area scarcely a single oyster was to be found. Yet the banks recuperated and became stocked wth countless millions of oysters. This rejuvenescence was certainly not due to their owir recuperative powers. At present the banks are barren all along the coast, and no oysters are to be found. This circumstance has often been repeated during historical times. From where do the exotic spat come, and what brings them ? With reference to the Tuticorin banks, it is easy to understand that should spat be liberated there when the south-west monsoon is light or moderate (when the current rul^s north), it is almost certain that the larvae would be carried away through the Paumben Pass into Palk's Strait, or further north along the Indian coast. If hberated during a strong monsoon, the possibiUties are that the westerly wind would drift them out into the gulf, where they would become involved in the oceanic current and be carried towards Ceylon. Moreover, we have seen that during a strong monsoon the oceanic current actually sweeps the Tuticorin beds. It follows from the nature of the currents tliat the Tuticorin banks receive no exotic spat, for, as far as we are aware, no other oyster beds exist round Cape Comorin. Moreover, their own resources are being continually drained, and it is not to be wondered at that they are improfitable. On the Ceylon side, and on the areas still mider Government control, it is well Imown that they arc markedly unproductive. Yet the bottom is veiy suitable, and a few scattered oysters have been found thereon from time to time. No Hving oysters occurred there when we inspected the area in March, 1909 (Part III., " Ceylon Marine Biological Reports "), and only three fisheries have been held south of Tallai\allu Point siiice 1800. They were aU held on the Chilaw Paar, and took place in 1803, 1815, and 1884. We beheve tliis sterility due also to the prevailing currents, which during the south-west monsoon either run south when the monsoon is strong, or north with the wind when moderate or weak. Local spat, whenever they occur, are swept away and lost. Moreover, the chances of this area being supphed with exotic spat are very remote indeed. It is only during an intensely strong and continued monsoon that the current penetrates far enough north into the gulf to sweep the Company's banks, and thus convey spat therefrom to the banks still mider Government control, and even then it is highly probable that such spat would be driven ashore. Their chances of receiving spat from South Lidia, whenever spat occurs there, is equally remote, for as we have seen, when the monsoon is only weak the currents on the Indian side run north and through the Paumben Pass. Even if a moderate monsoon persists, the easterly oceanic current which eventually reaches the banks still under Government control almost certainly does not sweep over the Tuticorin banks, or penetrates far enough north to allow of spat being drifted into it by the prevailing westerly wind. CURRENTS. 239 It is only when a strong moiisoon persists for some considerable time that the oceanic current penetrates far enough into the gulf to sweep the Tuticoriu beds. In that case the easterly current stretching across the gulf reaches the Ceylon coast well north of Tallaivillu Point, carrying with it sp.^t when present from the Indian side. Such spat appear to be dejiosited on the banks under lease, and to never reach the banks further south, as the distance in the latter case is too great (HO miles), and the larvse mature and sink long before the current reaches so far south. The pearl banks under lease which are situated in that beautifully i)rotectcd cul-de-sac at the extreme north-east of the gulf now call for particidar attention. Their productivity at times is marvellous, yet barren years intervene. Much of the barrenness is due to causes other than currents, but, on the other hand, it is quite certain that much of their productiveness is, a!id has been, due to the fact that they have been periodically stocked with exotic sjiat, which, added to their own inherent powers of production and recuperation, has more than amply satisfied the demands of rapacious men and predatory fish. They also owe much to their protected position, and a glance at the chart will serve to illustrate this fact. The only surface movements on this part of the plateau are entirely dependent on the wind. Except in very strong and prolonged south-west monsoon no real current exists, and the tendency is for spat liberated in the vicinity to be retamed thereon , and to be deposited near its source of origin. If strong monsoon persists, we have seen that the current penetrates further and further into the gulf until it sweeps the Tuticorin beds, and the possibilities are then tjresent for spat being brought across and deposited on the banks under lease. The same current turning south and following the trend of the land would also carry away to the south the local spat from the banks imder lease, but the likelihood is that such spat, instead of actually being deposited on the banks still under control, would merely drift ashore. On the more inshore areas, as on the Kondatchi Paar, succeeding spatfalls have gradually wandered closer iiifihore. The possibilities of the banks under lease receiving spat from the Indian side during a strong monsoon are very considerable, althougli as yet we only understand in merest outline a few of the factors which may conduce to bring about this result. If the south-west monsoon is Ught or moderate, the spat from the Indian side runs with the northern current through the Paumben Pass. It is evident that under these conditions no spat could possibly drift on to the banks under lease. It is only when the south-west monsoon is very strong and prolonged that the oceanic current penetrates further and further into the gulf, until eventuaUy it sweeps the Tuticorin banks. If oysters are present there, their spat is almost certainly brought across to the banks under lease by the current, which in strong monsoon most probably penetrates the gulf much further north than is indicated on the appended chart showing the residts obtained during 1910, when the monsoon was not either veiy strong or continuous. The absence of an exotic spatfall this year, as in other years, lias either been due to the moderate monsoon which prevailed, or to the absence of spatting oysters on the Tuticorin banks. The larvte of the oyster are pelagic, i.e., they live on the surface of the ocean for about the first five to seven days of their existence. They then develop a shell, and droi^ping tp tlie bottom become attached. There can be no doubt tliat many drop in deep water and are lost. The depth most suitable for oysters is 6 fathoms. The distance from the Indian banks to the banks under lease is approximately 85 mdes. Taking seven days as the maximum time occupied by the pelagic stage, a continuous surface drift to the east of 0-6 knot per hour for six successive days would place the spat on our banks. Wo boheve that this does hajjpen occasionally, but only during strong monsoon. Otherwise it would bo impossible to explain the -sudden transition from absolute barreimess to remarkable luxuriance which has characterized the area under lease through long periods of histoiy. Such in merest outhne are the conditions of the surface current over the entire plateau. No doubt there are other factors atM-ork, which subsequent research alone can elucidate, but wo feel satisfied that the results and explanations given above have a very real significance, and that the broad general facts are as above stated. Although our results this year distinctly prove that the oceanic current reaches tlic Ceylon coast south of Tallaivillu Point during strong monsoon weather, the results of another 24<) CEYLON MARINE BIOLOGICAL REPORTS. year might show that the current struck either a Httle north or south of the point in question. This, however, would not in the least affect the main facts of its existence and general direction. It is exceedingly unfortunate that in spite of all effects we have been unable to obtain any data regarding the oyster beds near Tuticorin. No systematic survey or inspection appears to be carried on round Southern India, and oysters are merely fished when present. Data concerning historical fisheries there (both recent and otherwise) M'ould enable us to collect important data regarding spatfalls, for the monsoon conditions are recorded yearly, and on the Ceylon banks we have records of times when in all probability exotic spatfalls occurred on our owii area. In the investigation of these superficial currents we have relied almost wholly on sets or part set^ of bottles which travelled quickly, or in bulk, as more Ukely to indicate the true nature and direction of the prevailing current and be free from extraneous and disturbing factors. Some bottles appeared to have had an erratic course, whilst others were, as expected, not recovered. However, the mass of the evidence was as given in the preceding pages. It is remarkable how the productivities of the paar areas coincide with the evidence afforded by currents. Both the Tuticorin banks and those south of TaUaiviUu Point are remarkably barren. This circumstance one would naturally expect to be the case on areas continually swept by currents at critical periods ; whilst on the area mider lease, not only are they protected and free from sweeping currents, but under certain circumstances they may even be replenished by spat derived from elsewhere. Apart from the general trend and sweej) of the oceanic current above named, there are, of course, innumerable minor and local eddies along the coast dependent entirely on the configuration of the land and the direction of the wind. They are in every case purely local , and in no way affect the general results just described. We, therefore, need not deal \rith them here, altliough we are cognizant of their existence. ^^'e append a Hst of the stations where bottles were hberated during each monsoon, giving percentage returns, stations, &c., together with exjilanatoiy charts (A, B, and C). We are strongly of opmion that drift bottles ought to be hberated in numbers every year over the Tuticorin banks during the spatting season. It is only by so doing, and by obtaining information regarding the condition of the Tuticorin beds at the time of liberation, that the question of exotic spat can be definitely settled and our results corroborated and enlarged uj)on. Even if the origin of exotic spat was fuUy and finally elucidated, the control of the elements in Nature producing the results would be beyond the power of man. As Steuart said in 1843 (" An Account of the Pearl Fisheries of Ceylon "), '■ the success of the pearl fisheries in the Gulf of Mannar depends primarily upon natural events beyond the control of man. Nevertheless, we may by the most vigilant attention and good management watch the progressive workings of Nature, and not fish up the oysters before they have reached maturity, nor, after they contahi the pearl, suffer them to die on the banks and the pearl to be lost We may presume from past experience that unsuccessful intervals mU continue to recur We camiot cause the spawn to settle down upon nourishing groimds. These are events beyond the control of man. The wand, the waves, and the uncertain currents of the ocean carry the embryo over unUmited space. It is only when in the infinite wisdom of the Creator of all things the oyster broods descend upon banks suited to nourish and support it that it comes within our hmited power to watch its advancmg age and to fish up the respective deijosits in succession " A knowledge of the true facts is, however, essential to successful culture, as they enable us to lay and mature our plans accordingly. III. — Bottom Ciieeents, Our knowledge concerning bottom currents over the plateau is confined entirely to the area under lease. Of the movements which the bottom layers of water may undergo on the ground still under Government control we have no information, and even on the northern area our knowledge is limited to the conditions existing during the north-east monsoon. These, however, give some indication of what the conditions must have been during the preceding south-west monsoon. From what has been said in the foregoing pages on the surface drifts prevalent over the plateau under lease, it is evident that no serious disturbance at the bottom could accrue from the conditions existing at the surface. The loss of oysters through a bottom current implies a current sufficiently strong to actually tear oysters from their anchorage. Steuart, writing in 1843 (" Account of the Pearl CURRENTS. • 241 Fisheries of Ceylon "), stated that '' there appeared to be no reason to beheve tliat the oysters were subject to be covered with drifting sand." Any one who has endeavoured to remove a mussel or an oyster from its attachment will understand that considerable force is required to effect this. A bottom current of sufficient strength to sweep away and entirely annihilate whole beds of oysters must indeed be strong. It would appear that the disappearance of beds of spat or adult oysters has been curiously mixed up with surface currents, or rather with surface drift. Whilst we attribute the disappearance to other causes, it is worthy of note that the distinction between surface current or drift and bottom current is most important. The oyster lives at the bottom, and the surface current or drift is only important in so far as it affects tlie bottorn, or in that it is the agency whereby spat is brought or carried away. It is of course possible on a small scale for a bottom current to be independent of the surface current. Our investigations, however, even though limited in extent, have so far tended to prove that the water on the bottom of the area in question is calm and that currents do not exist. There are movements in the water, but these movements are vertical and not horizontal ; they are gentle undulations, not currents ; and we have been unable so far to collect any evidence to indicate that a bottom current exists either during the north-east or south-west monsoon. It would appear likely that if bottom currents exist which are strong enough to remove oysters from their anchorage, the evidence relating thereto would neither be scanty nor rare ; but the dress-diving operations conducted by one of us over two seasons during the north-east monsoon has afforded no evidence of any current. It is well known that from time to time beds of oysters or spat have entirely disappeared and left no trace behind. This disappearance has in every case been attributed to bottom currents. Yet in no single instance has any proof been adduced that such was really the case. The disappearance was merely attributed to currents because no other cause seemed apparent. In Part IV. Report of this series it was there sho^vn that the annihilation of a bed of spat on the Periya Paar Karai, numbering 400,000,000, was due to predatory fish. The remains of the crushed shell on the area in question «'ere only obtained when the dredge was lined with canvas, and the debris even escaped the notice of the divers. When these catastrophes occur on a rocky bottom, the clue to the situation remains obvious for a long time ; but if it happens on sand, the broken shell gradually sinks into the sand and disappears. This circumstance is, however, not due to silting over by sand, but to the heavier shell debris gradually settUng. It thus becomes clear how it may happen that a bed of oysters disappear and leave no trace behind them. Whilst we are not prepared to -state that every bed which has been lost has been devoured by fish, it appears very probable from the analogous case just quoted that such was the case, and that the apparently entire absence of any remains led to the conclusion that the bed had been swept away by a current. It is impossible, however, with any degree of certainty to state why beds of oysters disappeared in the past. In this paper we shall deal with data collected during our oa^ti experience, and although our evidence is wholly negative, we recognize that bottom currents may have occurred spasmodically in the past, and may do so again, but during the last five years it is certain that none have existed or occurred. It might be argued that on a shallow water plateau, such as the one under lease, any degree of surface current must of necessity produce a bottom current. This is most Ukely true, but, as we have already pointed out, no surface current exists on the banks under lease. The almost regular appearance of spat on the Periya Paar, and its equally regular disappearance, presents an important question, which up to the present has not been sufficiently investigated. This bank is situated about 18 miles out at sea, towards the north of the plateau and due \^'est of Tuticorin. The depth of water is from 8 to 10 fathoms, and within a cable's length there are tlie overfalls (200-300 fatlioms). The spat so regularly found thereon are undoubtedly brought from the Tuticorin side by the oceanic current, whicli rmis east during the south-west monsoon. These spat usually disappear before the end of the following Januaiy (or during the north-east monsoon). The oceanic surface current which at this time runs west from Tallaivillu Point no doubt produces some bottom current on the southern shallow water plateau over which it sweeps, but a reference to the chart will show that the Periya Paar is well north (30 miles) of tlie point from which the current takes a westerly direction. The disappearance of 57-11 242 CEYLON MARINE BIOLOGICAL REPORTS. spat tliercforo from the Periya Paar is still veiy enigmatical, and the only conclusion one can arrive at iu the present state of our knowledge is tliat in some waj' or other it is incident on the proximity of this paar to the overfalls. It is further to be noted (i.) a large portion of this paar is sand, wliere oysters could not possibly live ; (ii.) owing to the immense deposits, largo numbers, even if occurring on rock, die from overcrowding ; and (iii.) that the bank is, par excellence, the home of large oyster-eating rays and teleosts, and is recognized as the best fishing ground on the entire plateau. Finally, it is worthy of note that only one fishery has taken place on this paar (1879). The bank lias been stocked w^th immense numbers of spat at least fifteen times during the last century, and in oveiy case they have disappeared when about three to six months old. The disappearance has always taken place during the north-east monsoon, and never during the south-west, and that in the only case where the spat survived the first six months and thus acquired a firm foothold they lived to be adult and provided a good fisheiy. This latter point is of very considerable importance, for it shows to us that if young oysters occurring thereon are swept away by bottom currents, once they obtain a foothold they are safe. This fact lends an interesting side light on the impossibility of older oysters (one to five years) being swept away by currents on more protected areas. Li now deahng with bottom currents on the plateau in general, it is to be noted that our information has been derived principally from three sources, and, as previoijsly noted, they refer only to the north- east monsoon and to the area under lease. (1) Rough measurements of the bottom currents were made during two seasons by means of the following apparatus : — A tow net was sunk by means of a small iron ring round the mouth to within 3 feet from the bottom. The depth over which the observations were made varied from day to day between 5 and 10 fathoms. Assuming the depth to be 6 J fathoms, the tow net was suspended by 6 fathoms of rope to a flat bamboo float at the surface. This was placed just astern of the ship and allowed to drift for one hour. The direction of the drift was noted, and the distance at the end of the hour measured. This was done three times per day during two north-east monsoons. The average rate of the current over the entire period was approximately 0-15 knot per hour. This method is of course far from accurate, for it was found that the surface float was acted upon by the surface wind and drift, and thus tended to drag the bottom net, which was but lightly sunk. The results were further comphcated by the fact that during parts of March and April dead calms prevailed. Only on one occasion was it found that the bottom current was running in an opposite direction to the surface current. The above results are of too crude a nature to count for anything, save that if a strong bottom current had existed the indication would certainly have been noted. (2) During the last six seasons (1906-1911) native divers have been continually at work on the banks. It is exceedingly difficult to obtain precise information from divers, but only on very rare occasions they have stated that there was a " little current " at the bottom. (3) The whole of the data on which we rely for our knowledge of the bottom currents has been obtained by one of us by means of the diving dress, and this work has been conducted over two seasons. Although, as noted, dress diving has only been carried on during the north-east monsoon, the bulk of the work was done very early, before the south-west monsoon had fully subsided, and when one would naturally expect to find the accumulated and undisturbed results of the monsoon on the floor of the ocean. It is on this account that we place some reUance on our data, for although our observations were not made during the actual south-west monsoon, stiU, if a bottom current existed for several months, there would certainly be some indication of it at the bottom, particularly over the sandy areas which here and there alternate with rock. This sand is divisible into two kinds : a loose, coarse-grained, angular kind, usually occurring on rock, and mixed with sliell debris, and a fine-grained kind. Usually they do not co-exist at the same place, but if thej' do, one kind is predominant. The fine-grained sand is more or less consoUdated, and is hard, and caked, and not yielding when trod upon. The coarse-grained angular sand may be considered as water-logged, for o\ving to its angular nature there are considerable interspaces between the grains filled with water, M-liich do not exist in tlie fine-grained variety. Consequently it is found, and has been proved over and over again by means of the diving dress, that the coarse-grained sand is more susceptible to bottom movements than the fine-grained sand. CURRENTS. 243 This fact is of some importance, for descents made over the banks on the heels of the south-west monsoon showed that here and there the coarse sand was thrown into ridges, usually — almost always — about 2 feet apart, 4 inches high, and facing south-west. These ridges could not be produced by a bottom current, for such a current would tend to drift the sand to the north-east and toward the land, the accumulated result of which over many centuries would ultimately sweep landward the whole of the sand and eventually leave a clean bottom. No such result has, however, taken place. The comiter effect of the north-east monsoon may be entirely neglected, for not only are the banks directly under the lee of the land, but they are further protected by a more or less continuous fringing coral reef. The production of these ridges is obviously due to the surface agitation affecting the bottom layer of water. But the bottom movement is vertical and not horizontal ; it is undulatory and not progressive. In other words, it is a wave and not a current. It has been previously slio\ra that on the area under lease the fuU force of the south-west monsoon is not felt owing to the penetration of the oceanic current, and consequently the bottom is almost calm. To the south of the plateau (on the area still under Government control) and on the west coast of Ceylon south of TaUaivillu Point, where the plateau is narrow and swept by an oceanic current during both monsoons, and where the water is shallow, it is most likely that a bottom current is usual. In fact, our experience on these banks corroborates this idea, and a sandy bottom is rare on these southern banks. Referring in particular to the area under lease, the banks to the south of the plateau, and including the Muttuvaratu Paars, are for the most part made up of dead coral, and sand only exists close to the shore. In the vicinity of Karativu shoal bottom disturbance is naturally more evident than elsewhere, due to the sweU breaking on the shoal. But this effect is purely local. On the southern extremity of the West Cheval there is also evidence of bottom disturbance. Here the rock is covered in places by a few inches of coarse sand mixed with shell debris, and this sand is thro^vn into ridges averaging 2 feet in length and 6 inches in height, leaving the rock bare between the ridges. In all cases the coarse sand is composed of angular quartz, oxidized on its outer surface, shghtly impregnated with iron, and of a yeUow appearance. The ridges all face south-west, and their sides are steep, suggesting tliat they can only have been formed by vertical motion. Apart from the vicinity of the Karativu shoal, there is little evidence of any disturbance. The rock is practically bare on the Mid-west, Mid-east, and North-west Cheval. The North-east Cheval is also very free from sand. On other area, such as the Periya Paar Karai and Vankali Paar, where the rock is covered in places by only a few inches of coarse sand, the ridges are usually 2 feet apart and up to 6 inches high. On the Moderagam Paar the ridges are 3 feet apart and only 2 inches high. On the real sandy wastes (in contradistinction to paar ground covered only by a few inches of sand) the sand, as we have seen, is fine-grained and very compact. The ridges over such areas are very slight indeed, and are never more than 1 or 2 inches high and about 2 feet apart. Besides the evidence afforded by the ridging of the sand, which aU over the plateau is on the small scale indicated, there exist numbers of crevices and holes on the floor of the ocean. In some cases these holes are caused by disintegrated coral having become dislodged, whilst in other cases they are natural configurations of the rock. Many of these holes are quite 3 feet deep, and one would naturally expect to find that if considerable movements in the sand took place, that these holes would eventually fill up. Yet they have often been examined, and never more than 4 inches of coarse sand found in them. On the West Cheval Paar, in 9 fathoms of water, the rock has been observed to terminate abruptly in places on the west seaboard with a drop of 2 feet on to a sandy bottom. Here, too, one would expect to find that if the sand was carried about by a bottom current in a progressive motion, the sand would silt up against such an elevation of the rock, particularly durmg the south-west monsoon. Further, during the drift bottle experiments carried out over many years on the plateau, many bottles sank on located positions. At least four such bottles were picked up several months afterwards lying on the sand in tlie position where liberated. 244 CEYLON MARINE BIOLOGICAL REPORTS. Tlio fftlleu beacon and tl\c tanks marking tlie shoal buoy position have been examined on several occasions by one of us in a diving dress for evidence of bottom movement. The tanks liave remained exposed to successive monsoons at least during the last twenty years, and there has been no segregation or piling up of sand. The three remaining tanks are as empty as when first examined two years ago, and stand on the bottom witli no piUng up of sand or evidence of scour such as might be expected. But the sand is heavily ridged. Tlio slioal rises verj- abruptly on the west from 9 to 4 fathoms, giving rise to a confused sea during the south-west monsoon, which breaks at times. So thathcre, if anywhere, one would expect evidence of bottom movement. The tanks, however, remain empty as when first examined, and stand on the bottom free from segregating sand. So that it appears that the ridging of the sand is due to vertical and not horizontal disturbance. The preceding facts indicate some of tlie reasons wliich lead us to the conclusion that bottom currents do not exist on the pearl banks under lease, neither during the north-east or the south-west monsoon. Inspection work is often commenced late in October, before the south-west monsoon has subsided. At such a time the bottom layer of water is invariably turbid. The cause of this turbidity has been microscopically examined, and has been repeatedly proved to be due to the disintegrated remains of sea- weed and Caulerpas. The turbidity renders it almost impossible for divers to see, but it subsides gradually as the north-east monsoon begins. This condition of the bottom water is by no means an entirely unhealthy condition, for it provides extensive organic material for oysters to feed upon. It has been suggested using a Nanson's currentometer for observations on the bottom currents during the south-west monsoon. Such a meter however would, we believe, in any case only give the rate of the current, and not the direction, or the varying directions. The utter impossibihty of mooring such a meter on the banks during the south-west monsoon wiU, however, be apparent to any one who is famiUar -vnth the conditions in the gulf during this monsoon. In addition to the preceding data, a further 927 bottles in all were liberated during 1907, 1908, and 1910. The results therefrom have, however, been discarded. Li the majority of cases the place where they were liberated is not kno'on. In otlier instances they were liberated between the monsoons, when no definite result can be expected; whilst tlie balance includes bottles liberated at unsuitable places, or under unsuitable conditions. The returns quoted in Part III., "Ceylon Marine Biological Reports," are not included in this report. The following table gives topographical returns and percentages : — South-west Monsoon. BolUes liberated north of Tallaicillu Point (inshore), 1908 and 1909. — Bottles liberated went ashore and form part of the 927 discarded. Bottles liberated south of Tallaivillu Point, 1910. — Liberated, 60; recovered, 49; percentage, 81 "6 per cent. Bottles liberated between Colombo and Tuticorin, 7970.— Liberated, 505 ; recovered, 242 ; percentage, 48 per cent, (practically). Total number of bottles liberated on tlie above positions, 1908 and 1910. — Liberated, 565 ; recovered, 291 ; percentage, 51 '5 per cent. North-east Monsoon. Bottles liberated north of Tallaivillu Point, 1907, 1908, 1909, and J9i0.— Liberated, 284 ; recovered, 48 ; percentage, 17 per cent, (practically). Bottles liberated between Colombo and Tuticorin, 1909. — Liberated, 74 ; recovered, 12 ; percentage, 16" 2 per cent. Total number of bottles liberated on the above positions, 1907, 1908, 1909, and 1910. — Liberated, 358 ; recovered, 60 j percentage, 17 per cent, (practically). Abstract. Total number of bottles liberated .. .. .. 1,853 Total number of bottles discarded Total number of bottles liberated at all stations dnrmg both monsoons Total number of bottles returned during both monsoons . . Percentage returned over both monsoons 927 923 351 38- 1 CURRENTS. 245 ^ a o o c o o so o o a -^ c M S3 03 a '3 II i OH „ § - S5 O 03 c8 ® 13 a o o : « gu .a 6 S o o < C30 o3 iS . OO o — ^ — -^ ill = -T o bxZ — o c ~ .- -"^ s ~.2 s g 8 > o o ill! . ». " -*j -*:> -*^ 01 ^ m M 03 0 S cs o o O O o « o u „ I § J - J 1 5 5 :§ ° 9 J3 ■3 .2 S; S 3 "5 B 00 _^ o Js J3 g o c O !^ = S ?; coo 03 O p p =3 S S S "S > > > s O O O § o o o > £ £ E o n1 S & o c3 > >ra o o .d S^U ' ;; . S i OS 08 S 3 C - - o3 -ki 3 i S o S i! » == '3 S ^ o* •= , -t= -s ^-"^ 5 cS oS-g 4J a o O , S S o (D p o i T3 C 03 O S — ■ S ^ — r^ CLj -H CO 0^ ■a- so > a .S e o l6 C J5 og o .2 O o 08 ■c.S ^ts x= § 03 O c « c 1^ I :3^ i; 08 o a 2 -a ^ O H © P SB > ffl o"^ § o o * S; O O _j , © © =3 5 > >>s ."S > o o o o © © P3PS d a a ° P ° ° § h © © 73 J § g s ^ > > '^ cs o o c a g g § P5P5 >1 m 3 ." O c3 ® is o -*^ - to e S w 5 o o o © © b4 33 t4 0:3 0 -Sic; S © © 0: ^ a a s ia ^^^ t*-i t*^ t_, C ,, O O o s i.l'.l'.^l g.s.a.sa S o o o 3 ^ ■> > > 3 ^ o o o Ph <;; ^ -S .^ Li ^^■^- OS S a a a 2 13 3 O ^ ■3 a a 3 H as o o (3 O Q.O a £ Ji- So 08 a 03 a Ph ■a a ^x J2 j:: J3 'J ^ .^ -1^ ,d 1 t, t. ;^ Li 0000 esse; 'C tS 'O "^ 0000 tH tH Li Li o © o o > > > > 0000 0000 O CD O > -3 C8 — 08 — I -< M— 1 a S =8 a i si O . feo 03 3 (S u h;j Pj '^ O C8 © -5 1-5 H, >-i >-> l-i ^ l-i l-i i-s «i m to m m ... 3 3 3 3 3 ^.j;. 60 to bC M to 3^3333 3 4S 44 4^ 4d 43 rt iq CO X (0 3 9 3 3 3 to bo to to t£ 3 S3 55. < o Ph o 12; M N N M « (N M 03 •PU C ■+J P3 . o o GO 3 03 O c3 .- - <3 ® . S ^ Oi 03 « > e ^ 3 03 ,? 3 Ei Ph •B . 3 . |§ £ =3 ^ Pj u o3 ^S |l o -3 3 C3 o! — CS 03 Eri ^ S i „ ~ > g S ■" ^ CO C t. ■ i£ d 03 03 -.^^ .sa§ t^ _ p o -^ C o ooooooooo fr4t,tjt;t-^pt* . _ © © ■ > > > > o " " O O " ~ _ © © ■ a a a t^ t^ X 00 o oo o C^ C3 S^ OS * * 1^ ^ S S S3 S ©©PS « " fl C3 3 QO 00 GO o o -o C5 CI ^ Oi U f- U t^ o3 £ cS o3 S n P S ;ri t4 t-i t4 © © © © PL4 [£4 E^ E^ CO CI Ci O^ 03 o o o o o Ci C^ Ci C^ C3 3 C o o IS , o o o 03 Oi Oi C3 l« !z;»^taSS g t4 ^ § § g > c c fS =3 03 CURRENTS. 247 Since the preceding report on the cui-rents prevalent in the gulf was ^vritten, 900 more drift bottles have been liberated at the same stations durmg the south-west monsoon of 1911. The results are similar to those obtained in previous years, which they fuUy coi-roboratft. This j'ear (1911), however, the monsoon was extraordinarily light, and the consequence was that the oceanic current from the west was feeble, and never penetrated into the gulf at all. Consequently there was no " head " of water in that region. The currents, therefore, ran to the north and through Paumbeu Pass. On one occasion, when the monsoon was a little stronger than the year's average, this oceanic cmTcnt, sweeping past Cape Comorin, caught a set of bottles liberated there. Passing in a south-easterly dii-ection, it reached the Ceylon coast a little to the north of Colombo, where it caught and swept south- ward a set of bottles liberated near Colombo. The interest of this fact is that bottles liberated off Tallaivillu and Chilaw about the same time were drifted to the north. This interesting result shows that the oceanic current Just reached Ceylon between Negombo and Colombo, and that only on one occasion. The monsoon during July was very light and the current on both sides of the gulf, that is, off Manapad cxnd Tutieorin on the Indian side, and off Colombo, Chilaw, and TallaiviUu on the Ceylon side. During the early part of August the monsoon freshened a little, and on this occasion bottles released off Cape Comorin were swept easterly by the monsoon ocean current, and were recovered on the south coast of Ceylon between Colombo and Galle. During the second week in August the monsoon fell light again, and the current off Cape Comorin and off Ceylon ran steadily north, imtil the monsoon finally died away in September. Strictly speaking, there was practically no south-west monsoon during 1911. Consequently the bottles ran generally north and were lost. Onty 23 per cent, were recovered, as against 51-5 per cent, last year. Theoretically, dming a perfect south-west monsoon, bottles liberated on the stations shown on the charts appended ought all to be recovered on the Ceylon coast. The strength of any south-west monsoon may be measured by the percentage of bottles recovered. The weaker the monsoon , the greater the percentage of bottles lost, and so with exotic larvae. Through the kindness of Captain Fysh, R.N.R., of the R.M.S. " Pahtaua," and Captain Dickinson of the R.M.S. " Putiala," we were enabled to collect plankton twice daily (5 a.m. and 7 p.m.) over the vicinity of the Tuticorm pearl banlis. A net was devised to take the collections whilst the ships were under full way. The net consisted of a conical brass wire framework havuig a J-inch mesh. It was made of woven brass wire, and was suitably weighted with a brass ring round the top. This frame- work was intended to support the tow net when the ship was under way. Inside this net was fixed and fitted a net of jute hessian to prevent the tow net proper from chafing against the brass. The tow net itself was fitted and fixed inside the jute hessian. Splendid collections were made. The tow net had to be renewed almost every day, but the jute hessian net usually lasted for thi-ee or four days. We recommend this form of apparatus for collections of plankton imder similar circumstances. A few oyster larvse were noticed in the plankton on July 28 and 29 only, and these were scanty. The experiment shows, however, that it is possible to obtain good plankton catches in this way, and thus to know whether the oyster larvse wMch give rise to exotic spatfalls on our banks are present in the vicinity of Southern India. The outstanding feature is however that, although oyster larvse may be present in enormous numbers round Southern India, no exotic spat can possibly reach our banks unless the south-west monsoon continues strong during the critical period. Tlie experiment during 1911 conclusively showed that, even if larvse had been abimdant, they would have drifted through Paumben Pass and been lost. Wlien oysters are present on the Tutieorin side, their larvse drift through Paumben Pass, or drop into the abyss on their way to the pearl banks, or successfully reach the p ateau, depending absolutely on the strength of the monsoon. As Steuart remarked, the factors controlling these natural events are at present bej'ond our control , but now that the facts are understood, we recognize that the intermittency of fisheries is dependent on the strength of the successive monsoons. We have often suspected that there were meteorological rhythm 248 CEYLON MARINE BIOLOGICAL REPORTS. concerned in these periods of blaxikness, and we should not bo surprised to find when the data comes to be cai-efully examined that this is so. The data already to hand appears to pomt to this conclusion. yPo Ce^-lon the interest of the Tuticorin pearl banks lies in their being the area potentially supplying spat to the Ceylon pearl l)a*iks. As such they merit attention, and it is to be hoped that succeeding workers will have means of investigating these banks. With that information, and a knowledge of the nature of the south-west monsoon for any particular year, it will be possible to predict with, a considerable degree of certainty whether an exotic spatfall has occurred on the Ceylon banks before the inspection has commenced. In conclusion, we would tender the grateful thanks of the Company to all who have helped in this investigation by liberating drift bottles, and our special thanks are due to Captain Fj^sh and Captain Dickinson for the interest, care, and trouble they took in the collection of the plankton over a period of two and a half months. Current Chari for South West Monsoon - A \/Jeqapaiant ■■ B0nk ^IxouJtna/ the eas/erly ^gi u>Ae» flie Soui'h Wi^st Moyisoon. ivas s/roi^q fratvi qi lo ZS'-l'Julii and aaatn Jrom 15'^ to ZS'^Jiuausi Igio ^ LilUc j^ isiyecii basses Jrts C Xtirkkam 12 10. II. Lilh: 5 C 0,-V.'tfa. Uai) y//. Current Chart for South West Monsoon - B. Wecfa/oalani Show.r.a oi ytortkerlu cufreni durmcj r. It rises out of 3 fathoms of \\ater, and is very abrupt on the north side. There are other striking changes taking place in Dutcli Bay. Several vei-y interesting characteristics were noted in Part III., " Ceylon Marine Biological Reports," June, 1909. The severance of Ipanti-\Ti island from Karativu has , taken place of late years. A shoaJ now marks the subsidence, and a sheet of water 2 miles in breadth separates the islands. Another remark- able change, concurrent probably with the subsidence, is that at the south-west extremity of Karativu full-grown trees of 3 feet circumference now stand in 9 feet of water at a distance of a cable and a halt from the shore. As these trees do not appear to be more than twenty years old, it is evident that the subsidence is recent, and probably still going on, for when Dutch Bay was visited last it was fomid that a new channel had formed north of the present southern extremity of Karativu, so that the island is again divided. The other striking change noted in the above Report was the formation of a channel, now a mile broad, cutting off Dutch Bay Land from Mutwal Island. The channel is still broadening, much to the sorrow of an enterprising Sinhalese fisherman, who has planted a coconut tope, which is slowly and surely being washed away by each succeeding monsoon. This new channel on the south probably accounts for the segregation of sand on groimd hitherto kept clean by the velocity of the ebb and flow of tide, as doubtless a smaller volume of water passes through the main entrance now than formerly, when only one channel existed. In the face of such rapid and striking changes Dutch Bay cannot be recommended as a safe anchorage, and should be entered with great caution. It is only available for vessels of very hght draught — not over 12 feet. The entrance to the bay must be approached from the south of the Bar reef, the passage between the reef and Karativu not being safe, as sandy shoals form there. Native craft frequently water from Ipantivu Island, where weUs have been sunk at the north-west extremity, off which a depth of 12 feet is found at a distance of four cables. The water is good. Portugal Bay affords anchorage sheltered from the south-west monsoon in 4 fathoms of water, with good holding groimd, the bottom being stiff mud. This bay has no hidden danger, and the soundings are very even. It is ordy useful as an anchorage. Marichchukaddi, 4 miles furtlier north-east — the fishery headquarters — affords good anchorage for hght draught vessels in 3 fathoms of water, and is sheltered from the fuU force of the south-west monsoon, although there is a very steep sea and considerable surf on the beach during the height of the south-west monsoon. A good leading mark when approaching Marichchukaddi is the northern bimgalow of the three built on a chff , in hne with a large conspicuous tree bearing east. This gives a leading line over Karativu shoal in 3 fathoms of water. The bimgalows are very conspicuous, more so than Dixon's tower, which latter stands three cables north. The top of the tower is 95 feet above low water. Both form conspicuous marks over the East and West Cheval Paar. At Marichchukaddi there is a good supply of fresh water from two reservoirs, one a quarter and the other three-quarters of a mile from the beach, but the water is not so good as that found at Silavatarai, which is obtained from concrete wells smik close to the beach, and from which water can be readily pumped into a water boat. Silavatarai Anchorage lays three cables south of an iron beacon erected lately on the Silavatarai coral reef, and is only used when calling for water. Of late a nursery — formed of expanded metal — has been erected under the shelter of this reef. The ground is flat rock covered with a little sand, and is not u safe anchorage. NAUTICAL NOTES. 251 Mannar South Bar Anchorage lays in from 2 to 3 fathoms of water : the latter depth is found 3 miles from the shore. The bottom is very shelving : the 2-fathom line is fairly close in. about seven cables from the beach. The only mark in making South Bar is one recently erected by Mr. Stevenson, the late Assistant Government Agent of Mannar. There are no port marks visible at South Bar. One has onlj'' the mark referred to above, which is a post 30 feet high painted alternate black and white. It is situated at the sea end of tlie South Bar road. Vankah lighthouse makes a good cross bearing with this mark. The anchorage is only available for smalU craft, which unload where the South Bar road ends at the beach. Dhoneys alone are able to across the bar. 'V\Tien making Mannar anchorage from the south, Talaimannar Point (which is very conspicuous) bearing north leads clear of the north-west extremity of the VankaU reef. The black and white post described above may be steered for when bearing east. 3. — Reefs and Shoais. Bar Reef is fittingly so called, as it Ues at right angles to the coast line immediately outside Dutch Bay, and at the southern extremity of the area imder lease. The reef is exposed to the full force of the south-west monsoon, and doubtless accoimts for the segregation of sand and the sandy elevation on Karativu north of the Bar reef, M'liich it shelters. The elevation occurs north of where the new channel has formed referred to under " Anchorages, Dutch Bay," and has an approximate elevation of 12 feet. The reef protects a considerable sea area north as well as Karativu Island, north of the sandy elevation mentioned. The passage between the reef and Karativu is not safe for other than small craft, as sandy shoals form, and the bottom is very imeven. The reef is formed of three coral patches, the south-west patch being the most extensive, and lying east and west. The other coral patches occur one on the north and one on the east. The three patches (all of which dry at low water) form a triangle, the base being to the south. The intervening space has patches of living coral in deep water, the coral nearly reaching the surface in places. A striking feature about this reef is that, although it forms a natural barrier and breakwater, the sea, however rough, never breaks on it. In the height of the monsoon it is invisible, except at low water, when the coral can be seen, but there is no breaking sea. This particular characteristic is shared by the Vankali reef, and is accoimted for by the coral extending out into deep water. A breaking sea only occurs where the coral grows and terminates in shallow water. The Bar reef in rough as in fine weather is invisible, except at low tide ; consequently, as it lies in deep water, it is dangerous to approach. To obviate this two iron beacons have been erected, one on the south-west extremity, the other on the south-east. The reef covers an area of about 1 square mile, and is formed principally of Turhinaria crater, which grows in dense masses , and which makes it aU the more surprising that such a solid barrier does not cause a broken sea. The position of the reef has been found to be slightly different to that on the original chart. The reef has been re-charted, and the position of the beacons on it are now sho^m on the new chart. Dutch Bay beacon bearing east leads clear of the southern end of the Bar reef. Karativu Shoal is a sandy shoal running north from the northern extremity of Karativu island. It narrows as it goes north, and deepens (which depression marks the channel across the shoal for vessels to Marichchukaddi drawing less than 18 feet). It then shoals again and broadens, terminating abruptly 10 miles north, where it deepens suddenly from 3 to 6 fathoms. The northern extremity is called the Shoal Buoy Position, and was marked at one time by an iron beacon, which, however, owing to the sandy nature of the bottom, did not withstand the strength of the south-west monsoon, and now lays at the bottom. The fallen beacon is buoyed when inspection work is going on, as the position affords a good southern mark. Deep di-aught vessels would need to round north of this position when approaching Marichchukaddi . 252 CEYLON MARINK BIOLOGICAL REPORTS. The shoal is clearly visible in line and clear weather ^ as the white nature of the sandy bottom niftki's tlie Avater a light green. At such times the fallen beacon sliows up as a dark sliadoAv, as do several tanks sunk on the same spot. Karativu tope and beacon can just be seen, which, together with Kutrimalle tower and Kellar obelisk, form good marks to locate the position. The sunken beacon mentioned above has been recently examined with a view to raising it, but it was found in a veiy bad condition. Such a beacon, with an iron tray between the legs at the base and hea^^ly ballasted with a lumdred tons or more of stone ballast, might perhaps stand the monsoon, but the position is very exposed, and the sand veiy coarse and loose. A station buoy meets all present requirements, and is removed at the end of the fishing season. Aripu JReef lies due west of Aripu tope, at a distance of 4 miles, and occurs on the edge of the inshore overfalls of a shallow water plateau of from 2 to 3 fathoms, which extends out from the shore, and starting at Kutrimalle Point sweeps gradually in a curve to the north-west, and finally west-nortli- west. The coral reefs commence off Silavatarai, and are named Silavatarai, Aiipu, and Vankah reefs. Silavatarai reef forms the southern extremity. These coral reefs, which extend in a north-westerly direction for a distance of 5 miles, cover an area of about 4 square miles, and terminate on the west in from 4 to 5 fathoms of water. On the north a deep arm of the sea rmis in towards Vankah, and divides Aripu from Vankali reef. The area on the inshore side of Aripu reef lias been examined Arith a view to finding a suitable area protected by the reef, for another uurseiy like the one imder the lee of the Silavatarai reef, where unfortimately there is only 12 feet of water ; but although deep water was found on the northern extremity of the Aripu reef, it is not protected sufficiently. The reef is made up of three groups of coral, including the Silavatarai patch, which dry at low water. Madrepore predominates, and occurs in great variety. On this reef the sea breaks in places, which is accounted for by shallow water, there being a depth of under 6 feet in parts. Vankali Reef lays off the port of that name and north of the deep arm of the sea mentioned as dividing this from the Aripu reef. It occurs on the edge of the overfall of the shallow inshore plateau, which here extends in a more westerly direction, and is at the northern extremity, 9 miles from the shore. Tlie plateau inside is shallow, i.e., 2 to 2| fathoms. The coral grows in dense sohd masses on the overfalls, and terminates on the west face in from 5 to 6 fathoms. The most massive growths occur in from 1 to 2 fathoms. The reef covers an area roughly of 6 square miles, and is 6 miles long. It terminates north, where the shallow plateau ends, and soundings deepen to 5 fathoms. The characteristic of the coral growth here is Turhinaria cincerens in huge masses, rising abruptly, and growing in separate dense growths with deep chasms between, which make walking over the reef (of which an extensive area dries at low water) a dangerous busmess, imless one is attended by a boat and companions, for one might get badly hurt by a sudden fall into the deep abysses, and as the coral overlaps, it would be an easy matter to fuid oneself fast under the overhanging edge. On this reef, as on the Bar reef, the sea does not break, due to the fact that the coral grows out into deep water. An iron beacon has recently been erected on this reef, which has been placed on the highest and densest part of the reef, and in a position where it is hoped it will stand. The structure is of railway iron, and is surmounted by a black baU 6 feet in diameter over an inverted triangle, which can be clearly seen 8 mUes. A beacon on this reef was necessary, as the only bearing available on the northern paars is Aripu tope, and a second landmark was much needed. 4. — Beacons and other LAiJDMARKS. Since the Company took up the lease of the pearl banks considerable additions have been made to the landmarks, in order to facihtate the location of the various paars and rocky areas. The positions of the conspicuous natural landmarks have been fixed, and the positions of the original marks verified and corrected where necessary. The beacons which the Company have erected are Kutrimalle, Karativu, and Dutch Bay beacons ; and of late the two on the Bar reef, one on the Vankali reef, and another on Aripu reef. NAUTICAI. NOTES. - 263 Other small iron beacons have been put up, one on the Silavatarai reef and three others in Dutch Bay. T^vo of the latter have fallen owing to erosion and the loose nature of the sandy bottom where they were erected. Besides the erection and maintenance of the above beacons, the Company have cleared Arxmakalu tower of encroaching forest growth and cleaned and whitewashed it, as also Kutrimalle tower and Kellar obelisk — all original landmarks. Kutrimalle and Arunakalu towers, both trigonometrical stations, have furnished a base for fixing all landmarks as far north as Aripu tope. These two marks are masonry towers, and are to be seen a considerable distance owing to their high elevation. Kutrimalle tower is 230 feet and Arimakalu 280 feet above sea level. Starting from the south, Dutch Bay Beacon marks the southern extremity of the Company's area. It is situated on Dutch Baj? Land, I mile north of the northern of the two conspicuoiis coconut topes mentioned mider "Anchorages, Dutch Bay." It is, like Kutrimalle and Karativu beacons, built of palmyra trees stepped in cement, and is 37 feet high from the base, which base is about 4 feet above low water level. The beacon is painted white. Karativu Beacon is situated at the north end of Karativu island, and forms, together with Karativu tope, a useful mark to locate the Shoal Buoy Position. As previously mentioned, it can be seen clearly as far south as Bar reef. The beacon is 40 feet high and is coloured black. Kutrimalle Beacon is situated on Kutrimalle Point, and has an elevation of 145 feet above sea level. It is painted black and white, one-third black from the top, the lower two-thirds white. The beacon, with Kutrimalle tower, makes a useful magnetic transit bearmg for compass adjustment, as also does Karativu beacon with Kutrimalle tower. The two beacons erected on Bar Reef mark the south-west aiid south-east extremities. The south- west beacon has a black ball 5 feet in diameter, the top of which is 18 feet above low water mark. The south-east beacon has a cask on top mth a cross below. The top of the beacon is 12 feet above low water mark. The south-west beacon can be seen as far north as Karativu or Kutrimalle tope. . Aripu Reef Beacon is situated on the north-west extremity of Aripu reef, and marks tlie deep water channel which lays between the Aripu and VankaU reefs. It is built of rail\pay iron topped with angle iron, and is triangular in form, having three uprights, which arc bolted together at the top ; the south and west sides are battered in and whitewashed. The beacon is surmounted by a staff and cross yard ; the staff supports a conical cask, and a conical cask hangs from each yardarm, the whole being coloured black. The beacon stands in 3 feet of water at low water, and has a height of 30 feet above low water mark ; it is clearly visible at a distance of 9 miles. The Silavatarai Reef Beacon marks the southei'n extremity of this reef. It is a small beacon, and only serves as a guide when anchoring to the south of it, which position forms the most convenient anchorage for watermg. The VankaU Reef Beacon is built of railway iron bolted together. It is .situated on the. highest and most compact part of the reef, on a spot where the depth is only 5 feet. The rails liave been driven through the coral well into the mud and securely bolted together. The beacon is surmounted with a 6-feet black ball, the top of which is 28 feet above low water ; below the ball is an inverted black triangle. The beacon is clearly visible to the naked eye at a distance of 8 miles, and forms a useful and mucb- needed mark on the northern paars. Kellar and Doric Towers — or more correctly obelisks — are both original marlcs, erected by Govern- ment on well-selected sites between Marichchukaddi and Aripu. They are visible all over the Cheval Paar. Aripu tope also forms a useful mark, and can be seen as far west as the Periya Paar, distant 16 miles. The VankaU Light Beacon, wliich is an iron structure, has been boarded up by the Company on the west and south side and whitewashed ; tliis was necessary, as owing to the nature of the structure it could not be seen by day from the banks, although the Ught at night is visible 11 miles. The beacon is now clearly seen a distance of 12 miles, and is, in conjunction with the VankaU reef beacon and tlie beacon erected on the Aripu reef, a most useful landmark for the northern paars, i.e., Periya Paar Karai and the true Vankah. It is also a valuable mark when making Mannar anchorage. The height of the beacon is 46 feet from the base. 254 CEYLON MARINE BIOLOGICAL REPORTS. The next landmark north of Vankali is Talaiinannar Point, on whicli the trees grow thickly and iiitl ivbruptly, gi^'ing a well-defined landniarlc and a useful guide for clearing the north-west extremity of ^'aukali reef, where the point is clearly \isiblc, altiiough distant 12 miles. Talaimannar Point is also a useful bearing, coupled with the southern extremity of Mannar island, which latter from tliis point forms a good mark, di.stinguishahle by tlio abiupt ending of the trees, to fix positions on Anaivilundun and Nadukadu Paars. It is proposed to replace the palmyra beacons, i.e., Kutrimalle, Karativu, and Dutch Bay, by masonry obehsks, as the palmyra beacons require frequent attention owing to the attack of white ants, and are therefore expensive in upkeep. Masonry obelisks require little attention, and are more conspicuous than beacons built of palmyra trees. 5. — Paars and other Rocky Areas. The C'heval Paar, noted as being an area on which more oysters have been fished than tlie whole of the remaining paar ground, has always been carefully watched and examined, as here, if nowhere else, oysters may be looked for. Since the last fishery this ground has been most searchingly examined, in the hope that some portion of the late rich harvest of fishable oysters might stiU remain. These hopes, as is well known, were not realized. During the course of this close examination of the rocky area, it became apparent that, although the paar ground \vas charted fairly correctly, several rocky areas slio-mi as separate paars were extensions of the main i^aar. We had also reason to beUeve that the paar ground on the north of the Cheval was more extensive than shown. Consequently, a rectangular form of inspection was adopted in i^lace of the old circular method. Tlie latter form left intervening unexamined spaces between the circles, and was open to great distortion owing to the difficulty the boats had of making a true circular course. The rectangular method of inspection means that the whole ground is examined, as each square abuts against the next. A greater area is covered daily, and the prevailing north wind can be utihzed to assist the boats, which work across the wind east and west, starting from the ^yindward or north side, where they are towed by the steam tender, which also picks them up on occasions, when the inspection is fiirished, to leeward of the shij»'s position and tows them back. This rectangular method of examining the ground (which, as is well known, is done by skin divers) combines inspection work with survey, for it shows the exact lay of the rrfck and the contour very closely, and has revealed considerable differences in the configuration of the Cheval Paar. The Periya Paar, and also the true Vankah, reveal similar difierences, the latter being a much greater area than is shown on the old chart. The Cheval Paar is formed of two large areas of rock. The one on the west, known as the West Cheval, is a compact, well-defined, oblong stretch of flat rock, only connected with the East Cheval by a narrow run of rocky gromid on the north. A narrow stretch of sand runs north of the Shoal Buoy Position (mentioned before as being the northern extremity of the Karativu shoal). This stretch of sand carries the same depth of water as the paar ground on each side, and is in no way a shoal. The old horseshoe configuration is consequently not correct. The flat rock carries on it heavy calcrete in the centre, living coral on the north, and coral ddbris to the south. The East Cheval has been found to have three extensions, wliich have been named northern extension, north-east extension, and south-east extension of tlie East Cheval. The East Cheval is also largely fonned of flat rock, calcrete, and coral debris, the latter predominating, as shown on the chart furnished. The northern extension is formed of heavy calcrete on flat rock, and it thins out north to cora debris, then sand. This extension appears to have been knovra as the old Aripu Paar, although it does not quite coincide with the original charted position of this paar, wliich position was found to be all sand. NAUTICAL NOTES. 255 Tlie north-east extension is of coral debris alone with sand, and was formerly charted as a separate paar lmo^vn as Kallatidel Paav. The south-east extension of the Cheval is of flat rock, heavy ealorete, and coral debris, and was known as the true Kondatchi Paar, and charted as a separate paar. The entire area of the West and East Cheval, with extensions, is approximately 21 square miles. The depth of water over the West Cheval is from 7 to 8 fathoms, and on the East Cheval 6 fathoms. The extensions average a depth of 5 to 5| fathoms of water. Tlie most productive part of the Cheval has been the south part of the East Cheval. The Moderagam Paar. — What has been known as the North and South Moderagam Paars, and charted as separate areas of rock, are practically a southern extension of the East Cheval, although separated from the latter. This area is nearly aU sand with scattered coral debris, so scattered in fact as to hardly admit of being described as paar ground. A long narrow run of coral debris which extends due west from the East Cheval alone lends itself to configuration as paar ground, although scattered coral debris Ues to the east and west. The rocky area lies in a deep water cul-de-sac, which i^robably aceomits for oysters maturing here. A bed of 6,000,000 oysters matured on the Moderagam and was fished in 1904. The depth of water here, as on the East Cheval, is 6 fathoms. The Periya Paar Karat. — This paar is a compact sohd stretch of flat rook which hes due north of the Cheval at a distance of 2 miles, the intervening area being sand. A peculiarity of this paar is the prevalence of large potholes, vaiying from 12 to 15 feet across and from 3 to 4 feet in depth, with overhanging edges. These holes are the resorts of numbers of fish. The existence of these holes is a striking proof of the absence of bottom cm-rents and silting, for it is evident that the holes would be full of saud, and would appear as sand patches if there was anv drift of sand. The prevalence of these potholes makes dredging difficult. The area of the paar is roughly 2 square miles , and the average depth 8 fathoms. Calcrete and coral debris occur on the flat rock, and a great variety of weed. The Periya Paar Karai figures largely in the history of the banks as being a paar on which oysters have frequently matured. It was on this paar tliat a bed of spat was found in November, 1908, which mifortunately was demohshed by predatoi-y fish , as was amply proved by the quantities of broken shell and shell fragments dredged up by the " Violet," and also brought up by divers. The next paar of importance is — The true Vankali Paar, which lays 2^ miles nortli-west of the Periya Paar Karai ; it is separated from the latter by a narrow neck of sand. A bed of spat also occurred on this paar in November, 1908, which was considerably larger than the one which was found on the Periya Paar Karai, but shared the same fate. The area of tliis paar has been found to be much more extensive than shown on the original chart. The paar lays roughly east and west. It is 3 miles long, and covers an area of about 6 square miles. The depth of water is 7 fathoms on the east ; it deepens to 8 and 8^ in the centre, and to 10 fathoms on the west, where it approaches to within 2 miles of the nortliern extremity of the Periya Paar. Two-thirds of the paar has a depth of under 9 fathoms. The paar is rouglily made up of flat rock, with calcrete and coral debris. There is an extension to the north of coral debris, which thins out, and is too scattered to chart as true paar ground. The whole of this paar is excellent ground for oysters. It is difficult to understand why it has not a better record, but it seems Ukely, as it is so closely adjacent to the Periya Paar Karai, that some of the fislieries attributed to the latter may have occurred on the true Vankah. The general characteristics of the West Cheval, the Periya Paar Karai, and the true Vankali closely approximate each other, the nature of the bottom and the average depth of water being the same. A northern landmark was much iieeded here. The beacons recently erected on the Vankali and Aripu reefs have met this want. The Kondatchi Paar occuis on an area — ^now known as the Kondatchi area — east of the Cheval, extending to the 3-fathom line, and reaching as far north as tlie Silavatarai reef, and south to the KeUar obehsk. Scattered coral debris is found over a considerable portion of this area, but it is too 25« CEYLON MARINE BIOLOGICAL RKPORTS. scattered to be charted as paar groimd. This scattered coral debris, togetlier with the occurrence of beds of Piimas, forms cultch on which oyster beds have frequently occurred and matured ; but the oysters, although large, are knoAm to be very poor pearl producers, incident on the aliallow water on vhich they occur, i.e., 4, 3i, and 3 fathoms, and the absence of infecting parasites. TJie Mttttuvaratu Paar comes next to the Cheval in productiveness. The Multavaratu Paar starts north of the northern extremity of Karativu island, on the edge of the overfalls, and extends south as far as Bar reef. Starting at the north, where the paar narro\vs to a point on the edge of the overfalls, it broadens south, and approaclies Karativu island to within a naile of the beach. It tlien runs roughly Boutli-south-west until the Bar reef is reached. The west is bounded by the overfalls. This extensive rockj' area includes— starting from the north — Karativu, Alan turai, and Krusadai Paars, also Hamilton's Muttuvaratu and Donnan's ]Muttuvar.atu, tlie whole being one continuous rocky area covering approxi- mately 28 square miles. This vast stretch of rocky area represents about 25 square miles of potential paar ground, the paars above named being those on which oysters have matured and been fished. The bottom is flat rock, on which quantities of massive Pontes grow, the ruins of which lie scattered ov»r the whole area, forming excellent cultch. Isolated growths of Turhinaria crater and brain coral also occur in great quantities, but the Madrepore ground is practically useless for oyster culture, and represents 3 square miles. To the south, just north of, and in the vicinity of the Bar reef, beds of Madrepore occur, which cover considerable areas. The feature of the paar north of the Bar reef is the absence of Madrepore and the large size and massive growth of Porites, which occur in groups and rise on their own ruins to 3 and 4 feet above the bottom, and is described by native divers as "peaky rock." These massive growths of Porites make dredging and trawling operations impossible over this area. With the Porites and other massive coral growths , such as brain coral, Galaxia, and Mussa, quanti- ties of Foraminifera and Halimeda occur, together vnth. a great variety of weed other than the latter. The depth of water on the inshore or east side of the paar averages 5 fathoms, which deepens gradually as the overfalls are reached to 9 fathoms, which is found on the edge of the overfalls, which here are very precipitate. The Muttuvaratu Paar ends the list of the historically productive jiaars. We now come to the great — Periya Paar. — This paar is situated on the edge of the overfalls from the 9-fathom j)lateau to the 14- to 20-fathom plateau, distant 18 miles from the land. A succession of plateaus occur off the coast at this point, i.e., due west and north of KeUar obehsk, starting with a 2-fathom plateau, with, a fall to the 4- and 5-fathom plateau, on which the Kondatchi Paar occurs, then again to 6 and 7 fathoms, on which the Cheval Paar is situated. After this we get a shght depression to 9 and 10 fathoms, which decreases to 8 and 9 fathoms respectively as the Periya Paar isa'eached. The Periya Paar lies on the edge of the fall from what may be termed the Cheval plateau , which gradually deepens from 6 and 7 to 8 and 9 fathoms until the overfall is reached to the 14- and 20-fathom plateau, which latter finally ends at the overfalls proper, where we get a precipitate fall to 100 fathoms or tuore. The slight depression noted between the Cheval and the Periya Paar resembles the depression or valley noted on the plateau off the south coast by Captain Somerville, R.N., in " Spolia Zeylanica," Vol. v., Part III., April, 1908. The average depth of water over the paar is 9 fathoms, deepening rapidly on the west to 14 fathoms. The paar on the south is about 2 miles broad, 11 miles in length, and tapers on the north to a fine point. The paar takes the trend of the overfalls on which it occurs, which here run in a north-west by north direction. The northern extremity of the paar approaches, as is noted elsewhere, to within 2 miles of the true Vankah Paar. The paar is represented by a rocky edge, on which Uving coral occurs on the north, but which has died out on the south, where there is a httle less depth of water, i.e., 7| to 8 fathoms. It was on the southern part that a bed of oysters matured which were fished in 1879, and this is the only fishery recorded on this paar. The importance of the paar is solely due to the frequent and almost seasonal occurrences of large spatfalls ; but only on the above occasion have oysters matured here. NAUTICAL NOTES. 257 Anaivilundun and Nadukadu Paars are the most northern, and represent one continuous stretch of rocky groiuid ^rith living coral, coral debris, and weed. The paar is situated on the edge of an overfall, from a 5-fathom plateau to a 7 to 8 fathoms, which is a continuation of the overfall on which the Vankali reef occurs, although the reef ends where the 2-fathom plateau between the reef and the coast terminates. The above 5-fathom plateau extends out in a southerly direction from Adam's Bridge , and is formed of mud and fine sand, with patches of living coral and quantities of prawns and shells. The paar itself is formed almost wholly of Turhinaria crater. Massive stony coral is rarely found here. The area of the paar is considerable, being approximately 6 square miles. The average depth is 5 fathoms. There appears no record of oysters maturing or of fisheries on this paar, although the rock where the coral occurs is clean and apjiears suitable for oysters. The paar is about 6 miles long and 1 mile broad, and rims in a west-north-westerly direction from Vankali reef, from which it is separated by a 3-mile stretch of sandy bottom, on which the depth of water increases as the Vankali reef is left and the paar is approached. 6. — Method of Inspection by Divek.s. The examination and inspection of the pearl banks is carried out by native divers imder the superintendence of the Superintendent of Fisheries, who also checks and verifies the native divers' reports as to the nature of the bottom by personal inspection in the diving dress. The present method of inspection is an improvement on the circular method inaugurated by Capt. Donnan, which latter necessarily left intervening spaces between the circles, to obviate which the present rectangular method has been adopted. The circular method was convenient for prospecting, but for systematic survey and accuracy the rectangular method adopted has many advantages, such being continuity, greater accuracy, and the avoidance of distortion, equahzed labour, and a greater area covered daily ; the courses are straight, and full advantage can be taken of the prevaiUng north «"ind, and finally four areas can be inspected from one central position, which means that the inspecting vessel need only move to a new position every third or fourth day. The latter advantage is a great saving of wear and tear to the Company's vessels. Another advantage of the rectangular method is alinement, which means that lines of positions can be extended to the outside positions with great accuracy ; and a further advantage is that beds of oysters can be, as the paar is, accurately figured and the numbers estimated more nearly. The four inspection boats, six-oared whalers, start from the ^^indward side of the area to be inspected, and work across the wind east and west, between the buoys (which are laid down north and south, east and west), in such a manner as to direct the boats on their east and west course and prevent their getting out of position. Each coxswain is provided with a chart on which the result of each dive is recorded with the soundings. The inspection chart is divided into six sections ; the top or north one is known as No. 1 section. Starting, we will say, from the north-west buoy, the four boats take up their positions and proceed to take a line of dives as they go east. The north boat steers for the north-east buoy, and the south boat for the intermediate north buoy of the centre line of buoys. The centre intermediate line of buoys are laid as a guide to prevent the boats getting set to leeward. No. 1 boat (No. I coxswain) takes the windward position and No. 2 (No. 2 coxswain) the lee, and these coxswains are responsible for keeping position. Fourteen dives are made from each boat, and as they go across the area six times a total of 336 dives are made over the entire area. An area covers 2 J square miles, and represents a 9-mile course from each boat, although with turning and getting into position for each section the actual distance is 10^ miles. The boats are towed into position or back according to the ship's position. Each boat has a crew of six boatmen with three divers and two linemen, which, together with the coxswain, makes a crew of twelve. The inspection work starts at 7 a.m. , and an area is inspected by 1 p.m. , the inspection occupjring six hours, and each section one. The same area inspected by dredge occupies four hours. The smaller charts known as coxswain charts are filled in by each coxswain as each dive is made, and it is from these that the inspection chart is drawn up. 57-11 258 CEYLON MARINE BIOLOGICAL REPORTS. Such, in brief, is the present method of inspection, which has led to the more accurate charting of the rocky areas knowTi as paars, and. as pointed out above, also gives the correct configuration of oyster beds as well as the rock. 7. — Gener.'VL Observations and Remarks. On \-isiting the pearl banks for the first time one is struck wth the distance which the banks pi-opev — such as the Cheval Paar — are from tlie land, and tlie featurelessness of the coast, which is here very low-lying. The only conspicuous well-defined landmark is Kutrimalle Hill. The absence of other landmarks has been remedied by the erection of masonry towers, obelisks, and, of late, beacons, as described else- where. All landmarks are clearly seen after noon, but owing to the low elevation of the land, station or position buoj's have had to be used to iirolong hues of positions to the more northern paars in order to ensure accuracy. On such distant landmarks a sHght error means perhaps half a mile out where an object is from 14 to 20 miles distant, as in the case on the Periya Paar Karai and the true Vankali Paar. Here a system of alinement and transit bearings has been adopted, together with masthead angles, ensuring accuracy where the landmarks are so distant ; but we have the two new beacons, i.e., Aripu and VankaU reef beacons, to work \rith. On the southern paars, i.e., those south of Kutrimalle Point, starting from the northern extremity of Karati vu Island , this difficulty ceases , as the mainland has a good elevation. The paar groimd , includ- ing the Karati vu, Alanturai, Krusadai, and Muttuvaratu Paars, is bounded on the west by the overfall, which here approaches to wthin 6 miles of Karati vu Island, so that all landmarks are clearly visible, both those on the mainland and on Karativu Island. All nautical data accumulated during the last eight years, together with that obtained from the Admiralty chart of the Gulf of Mannar, the latest Government chart of the pearl banks, and other data obtained personally, has been co-ordinated within the last year, and are sho-mi on a preUminary chart which has been drawn up of the whole area imder lease. This chart embodies aU nautical data collected up to date, and also shows the paar or rocky gromid as revealed by the latest inspection, which, with the rectangular method of inspection as described, took the form of a survey. The chart also shows the fauna of the entire area, which has been determined by the Scientific Adviser to the Company ; it is therefore a nautical and biological chart. I may mention here that the positions of aU landmarks have been fixed and verified from a base hue between Armiakalu and Kutrimalle towers. The positions of these trigonometrical stations were furnished by the Government Survey Department on the latest chart of the pearl bank area. In addition to the above, a survey has been made of Dutch Bay, and a chart on a scale of 4 inches to one nautical mile drawTi up. Investigations on superficial currents in the Gulf of Mannar and immediate vicinity have been uiade and are being continued, which we have every reason to beheve are of considerable importance, and wiU throw more light on the origm of exotic spat, which from time to time replenish the banks, the intermittency of wliich accomits for the failure of fisheries. These investigations are being made from independent data, together with information obtained from the hberation of drift bottles and the collection of planktonic forms over long periods of time. An experimental nursery has been erected in the sea, under the lee of the Silavatarai reef. Un- fortxmately the depth of water is only 12 feet on this protected area. The nursery is built of expanded metal with railway iron uprights. It has %\ithstood the south-west monsoons well, and answers aU the purposes for which it was intended. A masonry tank has been erected on the foreshore at Marichchukaddi , and is' filled by a pump fitted with a filter. The pipe is carried well out clear of the foreshore into deep water. A second tank has been also fitted, and apphanees — drain pipes, &c. — such as are necessary for the experimental scientific work carried on. During recent trawUng operations for certain fish required for scientific experimental work the small number of fish on the banks at present was apparent, and is incident doubtless on the absence of oysters and other shell fish. CESTODE PARASITES. 259 No. 22. A DESCEIPTION OF TEN NEW SPECIES OF CESTODE PARASITES FROM MARINE FISHES OF CEYLON, WITH NOTES ON OTHER CESTODES FROM THE SAME REGION. By T. SOUTHWELL, A.R.C.Sc. (Lond.), F.L.S., F.Z.S. With three Plates. Trawling operations were continued, as usual, during the past year. The area under lease over which these operations were carried out cover the greater part of 700 square miles. At the jjresent time fish are by no means abundant, a fact which is undoubtedly connected with the absence of suitable food. "Shell fish" are remarkably scanty. Five years ago, wlien both oysters and other shell fish were abmidant, fish were much more plentiful. All the fish caught have been carefully and systematically exammed for cestode parasites, particularly the Elasmobranchs. No adult cestodes have been found in any Teleosts, but cysts are very numerous in most species, and a few are described in the present paper. The habitat and the larvje of the fdult cestodes described from the pearl banks are generally not known. Most probably this is because they have not lieen sufficiently carefully searched for. It is almost certain that the larvae of the adult forms described will be found later in tlio various Crustacea and molluscs. No parasites have been found in the flesh of any of the Teleosts examined. All the cj^sts obtained were found in the mesenteries, save in one case, where a few were discovered along with some Trematode redia (which measured about 20 mm. by 8 mm.) on the walls of the air bladder. The position of the encysted forms found in Teleosts, with relation to the Ufe-history of the parasite concerned, is very enigmatical. I am confident that in some cases these bony fish are merely parallel hosts, and that the life-history of the parasite is direct from the crustacean or molluscan host to the Elasmobranch. In some cases it may be found later that the mfoction of the Teleost is initial, and that the life-history is direct from the Teleost (particularly if this is a small form) to the Elasmobranch. The fact that no adult cestodes have ever been found in Teleosts lends favour to this theory. With reference to the life-history of the pearl-inducing worm itself (Tetrarhynclius unionijactor) no further light has been adduced, but it seems practically certain that the life-history is dhect from the oyster to the various Elasmobranchs whicJi devour them, and that Balistes, Serranus, and possibly other genera of fish represent subsidiary or parallel hosts. During an examination of Taniblegam Lake, which I recently made along with Dr. Pearson oi the Colombo Musemn, a few Trygons of various species were collected. In one .species a few adult specimens of Tetrarhynchus unionijactor were obtained. There seems little doubt that the pearl-inducing larvae. 260 CEYLON MARINE BIOLOGICAL REPORTS.' of PlaciiiM placenla is the same as in the pearl oyster, but tlio occurrence of tlxe adult in a Trygon was surprising, as tlie adult form is so very rarely found. A few of the genera, and many of the species, of cestodes described by Shipley and Hornell from the pearl banks have not been obtained by me. I append to this paper a full list of the cestodes obtained by me from the pearl banks, and a comparison of this list with that of Shipley and Hornell (20) will show which genera and species I have not obtained. I also append a list of parasitic Crustacea. Trematodes, Nematodes, &c. (mostly new species), ooUectied during the last five years, which await description. Owing to my leaving the services of the Company this paper has been prepared hurriedly. Few anatomical details have been dealt with, but it is hoped at some future time to fully describe the anatomical details of all the species dealt with, both in the present and in the preceding Reports. In general, the classification adopted in this paper is that followed by Linton. According to this author, the pearl-inducing worm is a Rhynchobothrium. The relations of the genera Rhinehothrium and Echeneihothrium require re-investigation, and our species Rhinehothrium Mpleyi, n. sp., appears to require a new genus. Larvae of the genus Otdbothrium are exceedingly abunds^nt in the Teleosts found on the pearl l>anks, and it is very remarkable that only a few adult specimens have ever been collected, and these only recently. In the present paper ten new species are described, and notes on seven other species are included. A note on a huge species of Trematode from Diagram-ma crassispinum is also added. The following is a list of the species described : — Acanthohothrium herdniani, n. sp. Platyhothrium spinulijera, n. sp. Anthobothrium floraformis, n. sp. Anthobothrivni ceylonicum, n. sp. Orygmatohothrium tetraglohum , n. sp. Rhinehothrium shipleyi. n. sp. Spongidbothrium lintoni, n. sp. Syndesmobothrium filicolle. Tetrarhynchus gangeticus. Otdbothrium insigne. Otdbothrium linstowi, n. sp. Rhynchobothrium, sp. I. Larvse. Rhynchobothrium , sp. II. Larvae. Rhynchobothrium, sp. III. Larvae. Rhynchobothrium, spp. A, B, and C. Larvae. Rhyncfwbothrium rossii, n. sp'. Paratcenia elongatus. n. sp. Trematode, sp. I am indebted to my former Assistant, Mr. George Morrison Henry of the Colombo Museum, for all the drawings which illustrate this paper, and also for the descriptions of two or three species, and I tender my grateful thanks herewith. I would here correct an error made in Part V. of these Reports. The first cestode material from the pearl banks was collected principally bj- Mr. Hornell, and was described by Professor Shipley and Mr. Hornell, and not by Professor Herdman. AcANTHOBOTHBiUM, Van Beneden. Body articulate, tseniaeform. Head separated from the bodj' by a neck, quadrangular. Bothria four, opposite, attached to head by antero-dorsal side, neck with two transverse costae on face and armed in front with two bifiu"cate hooks, and surmounted in front of hooks by a triangular pad bearing a sujiple- mental disc which is capable of assuming diverse forms. Genital apertures marginal. (Linton U.*) Acanthohothrium herdmani, n. sp. (Plate I., Figs. 1, 2, and 3.) Measurements. Extreme length Extreme breadth (at about f of the extreme length of the head) Length of head Breadth of head Length of terminal proglottid Breadth of terminal proglottid * These numbers refer to the literature cited at the end of tliis paper. ll (20) I have not obtained. The other cestodes have been collected from the sources named. A few specimens were obtained from the Indian Museum. Calcutta. Probably most of the parasitic Copepoda, Trematodes, aTid Nematodes collected are new species, and it is lioped that these as well as the other material named will be worked out and described at some later period. General. From Ticks Tesludo elegans. Solitary corals, n. spp. Ceylon pearl banks. Ualimeda gracilis in fructification Cej'lon pearl banks. Dermal cj'sts Testudo eUgaiis. Intra-uterine embryos, yomig Trygon kuhli. Do. slightly older ^ do. Do. Bhynchobatus columnce. Worms Coral. Sarcocystis tennella Muscle of buffalo. • Eclmwrhynchus tenor . . Scops bakkuamun (owl). Do. n. sp., with cysts . Lungs of rat snake {Zamenis mucosus) . Do. n. sp. Aster badius. PaBASITIC CRUSTACEA. CymothooB, n. sp. Serranus undulosus. Do. n. sp. . . do. Ciliciccea lattreilli (?) . . White Leptoclinid. Gnatliia, n. sp. Gills of Trygon kuhli. Do. n. sp. . . Galeocerdo tigrinus. Do. sp. Urogymnus asperrimus. Ecto-parasitic Copepoda Trygon kuhli. Do. Tceniura melanospilos. Parasitic Copepoda . . Bhynchobatus columnce. Do. Root of mouth of Lutjanus gibbus. Do. Serranus imdulosus. Do. Lutjanus argentimaculatus. Do. Gills of Rhynchobatus djeddensis. Do. Tceniura melaiwspilos. Nematodes. Filaria digitala (?), Von Linstow Bos indicus. Nematodes Tceniura melanospilos. Do. Chiloscyllium indicum. Do. Lethrinus miniatus. Do, Galeocerdo tigrinus. Do. Varanus, sp. Do. Turtle (Chelonia midas). Do. do. ( do. ). Do. Myliobatis nieuhofii. Do. .. Pristis cuspidatus. Do. Chorinemus lysan. Do. Urogymnus asperrimus. Do. Tetrodon stellatus. Nematode cysts Caranx, sp. Do. Caranx melanpygus. Nematodes in large cysts Nematodes A)iaporrhutum largum. . Ampliist&ma conicus . . Parawpliistomuin hath ycoiyle SchistorcJiis carneus Tiematodes Do. (Ecto-parasites) Do. Trematodes with Redia Trematode Trematode, 3 specimens 15 ui. long Redia and Trematode . . Solenophonis megalocephalus Do. Tmnia globipunctala Tcenia serrata Do. Do. Taenia serialis Chitlotmnia hursaria Dutheria fimhicata PlagiotcBiiia gigantea Pterocercus, spj). Cyslicercus pisijormis Cystkercvs fasciolaris Do. Gaenurus serialis Cyslicercus polymorphus Cyslicercus cellulosce . . Echinococcus polymorphus A Cj^st {Echinococcus polymorphus) (?) Dipylidium caninum Hymenolepis, n. sp. Tcenia marginata Tcenia, sp. Davania, n. sp. Davania polyalcaria Davania, n. sp. Do. sp. Do. sp. Oragmatoholhrium tetraglobum, n. sp. Cyclobolhrium typicum Adclobothrium cetohatidis Thysa n ohoth rium uarnakense Acanthohothrium, herdmani, n. sp. Platyhothrium spinulifera, n. sp. Prosthecobothrium Irygonis CESTODE PARASITES. From Bos indicus. Diagravmia crassispinum. 275 Trematodes. Cestodes. Chiloscyllium indiciim. Bile duct of buffalo. Bos indicus. Tetrodon stellaius. Jitobatis narinari. Chelonia viridis. Pinna bullata. Tetrodon stellaius. Diagramma crassispinum. do. Diagratnma, sp. Felis tigris. Python reticulalus. Sheep. Wild jackal. Felis tigris. Nesokia bengalensis . Dog. Lepas ruficauduttis. Varanus exanthematicus. Rhinoceros unicornis. Bentorphis pictus. Mus rattus. do. Rat. Goat. Bos indicus. Human brain. Goat. Bos indicus. Rat (Dog ?). Corvns macrorhynchns. Bos indicus. do. Centrococcyx rufipennis. Corvus macrorhynchus. Petragopeis gurial. Tockus gingalensis (hombill). Corvus splendetis. Ehynchobalus djeddensis. .Etobatis narinari. Rhyncliobatus djeddensis. Trygon icalga. Trygon kuhli. Galeocerdo tigrinus. Trygon kuhli. 276 CEYLON MARINE BIOLOGICAL REPORTS. SjiongiobotJiriiim lintoni, n. sp. Sjioiuiioholhrium iwiahilc Si/ndcsmoloth it u m fiUcoUc Dibothriiim hastatiis Dibothrium. sp. Otobothrium linstoici. n. sp. Cysts eontaming Otobothrium insigtie Echinobothrivm rhinoptera Ech inobothrvu m boisii Myzocephalus narinari Do. I'hi/Uobothroides hutso7ii Phyllobothroides kcrkhami Do. Rhinebothrmm flexili . . Rhin ebothrium ceylonicum Do. FJmiebothrmm shipleyi, n. sp. Calliobothrium eschrichtii Do. Calliobothrium filicolle Calliobothrium fanneri Echeneibothrium simplex Echeneibothrium iiisignia Echeneibothrium tvalga Anthobothrium pulmnatum Anthobothrium ceylonicum, n. sp. Anthobothrium floraformis , n. sp. Antliobothrium crispum AntJiobothrium laciniatum Tylocephalum varnak . . Do. Tylocephalum trygonis Tylocephalum kuhli Tylocephalum dierama Do. Cephulobothrium variabilis Do. Cephalobothrium cetobatidis Do. Cephalobothrium abruptum Do. Phyllobothrium lactuca Do. Phyllobothrium blakei = Anthobothrium Phyllobothrium foliatum, n. sp. Phyllobothrium pammicrum Larvae of Bhynchobolhriiim, sp. Tetrarhynchus larvae from cysts Tetrarhynchus unionifaclor Do. pulvinatum (?) From Rhynchobatns djeddensis. Trygon kuhli. Cybi^im guttatum. Trygon kuhli. Sterna bergii. Pristis cuspidatus. Diagramma crassispinnvi. Trygon kuhli. Aitobatis narinari. Chiloscyllium indicum. Galeocerdo tigrinus. Ginglymoslonia concolor. Chiloscyllium indicum. Ginglymostoma concolor. Pristis cusjndatus. Chiloscyllium indicum. Trygon kuhli. do. do. Chiloscyllium indicum. Pristis cuspidatus. Trygon kuhli. do. do. do. Mtobatis narinari. Trygon hddi. Carcharias, sp. Trygon walga. Carcharias bleekeri. Trygon kuhli. Trygon, sp. Trygori kuhli. do. do. PterojAatea micrura. Trygon kuhli. Pristis cuspidatus. do. yEtobatis narinari. Trygon kuhli. Pteroplatea micrura. Galeocerdo tigrinus. Trygon kuhli. do. Rhynchobatus djeddensis. Urogymnus asperrimus. Lutjanus argentimaculatus. Trygon walga. Ginglymostoma concolor. Urogymnus asperrimus. CESTODE PARASITES. 277 From Tetrarhjnclms unioniiador .. ■■ Trj/gfow, sp. (Tamblegam). Tetrarhynchusleucomelanus .. ■■ Trygon icalga. Do. ■■ • • Trygon sephen. 2)0. • • • • Rhynckobahis djeddetisis. Tetrarhynchus macrocephalus . . • • "''• Do. ■ . Trygon walga. Teirarhynchm ruficoUis ■■ ■ ■ "°- Do. ■ ■ Trygon kuhli. Tetrarhynchns rubromacvlatus . . "<'• Telrurhynchus spinvlifera .. •• Rhynchobaltis djtdaemis. Paratcenia elongatus, n. sp. . . Trygon kuhli. List of Literatxjre cited. (1) Braun.—Ia Bronn's Thier-reiches " Wumer," 1900. (2) £eH7(am.— Oxford. Zoology, Part lY., Platylielmia Mesozoa. Nemertini, 1901. (3) Van Beneden.—TlecheTches siir la Faime litterale de Belgique les Vers Cestoides. Men Ac. Belgiqiie, XXX., 1850. (4) Van Beneden.—Memoire sur les Vers Intestinaux. Paris, 1858. (5) Fuhrmann.— Swedish Zoological Expedition, Part III., Die Cestoden der Vogel des wiessen. Nils. 1909. (6) (?a«i6k.— Cambridge Natural History, Vol. II,, Platyhelmithes Mesozoa, 1896. (7) Johnstone.— Vomteenth Annual Report, Lancashire Sea Fisheries. Kab. Ti-ans. Liverpool Biol. Soc'.. Vol. XX., 1906. . ^ rn t- i (8) Jo/^Mstome.— Fifteenth Annual Report, Lancashue Sea Fisheries. Lab. Trans. Ln^erpool Biol. See, Vol. XX., 1907. .,_ m. t- i (9) ./o/*«sto»e.— Eighteenth Aimual Report, Lancashue Sea Fisheries. Lab. Ti-ans. Liverpool Biol. Soc, Vol. XX., 1910. (10) Von Linstow. —S^o]i& Zeylanica, Vol. in.. Part XI., 1906. (11) I^nioM.— United States Fish Commission, 1886 and 1887. (12) Linton — Proceedmgs of the United States National Museum, Vol. XX., 1898. (13) Xmton.— United States Commission of Fisheries. Fish Parasites coUected at Woods Hole, 1898. Washington, 1900. ^. , ^ xi. n, j n i« (14) ii«to».-United States Commission of Fisheries. Parasites of Fishes of the Woods Hole Region. Washington, 1901. .„ , ^ xt _,., n i- (15) Linton.-Bulhtm of the Bureau of Fisheries. Parasites of Fishes of Beaufort, ^ortll Carobna. Washington, 1905. ^ . . ,, . -p j (16) lAnton.-Buaetin of the Biueau of Fisheries. Not«s on the Flesh Parasites ot Marme Food Fishes. Wasliington, 1910. . . x.. t>i u f au (17) Linton.-BxiWetm of the Bureau of Fisheries. A Cestode Parasite m the Flesh of the Butterfish. Washmgton, 1907. . . T^• ^t r v.. Ti lonfi (18) ifok/.— Annuarie del Museo Zoologico deUa R. Universitia Di Napoh, Vol. il., iwo. (19) A^e«»iaMri..— Parasites and Parasitic Diseases of Domestic Animals, 1892. (20) Shipley and Hornell—Herdman's Ceylon Reports, Vols. II., HI., and V. (21) Shipley. —S/Vii\ej's Zoological Results, Part V., 1900. (22) Shipley.— iiTpoha, Zeylanica, Vol. I., Part III., 1903. (23) SoMiAweZZ.— Ceylon Marine Biological Reports, Part v., 1911. (24) Southwell.-Svo]i2. Zeylanica, Vol. VII., Part XXVII. (Ceylon Pearl-inducing Worm) , IQIL (25) Southwell.-SvoU^ Zeylanica, Vol. VII., Part XXVIII. (Ceylon Cestodes) 1911. (26) Z*c7*o/l-yfce.-Recherches sur la structure anatomy et histol des Cestodes. Men Instit. Nation. Genevois. XVII., 1886-89. 27S CEYLON MARINE BIOLOGICAL REPORTS. Expi^NATiON OF Plates. Fig. 1 Fig. 2 Fig. 3 .. Fig. 4 Fig. 5 .. Fig. 6 .. Fig. 7 Fig. 8 .. Fig. 9 .. Fig. 10 Fig. 11 Fig. 11a .. Fig. 12 Fig. 13 .. Fig. 13n . . i'^g. 14 Fig. 15 Fig. 16 Fig. 17 Fig. 18 Fig. 19 .. Fig. 20 .. Fig. 21 .. Fig. 22 .. Fig. 23 .. Fig. 24 Fig. 25 .. Fig. 26 .. Fig. 27 Fig. 28 .. Fig- 29 .. Fig. 30 .. Fig. 31 .. Fig. 32 .. Fig. 33 .. Fig. 34 Fig 35 .. Fig 36 .. Fig 37 Fig 38 Fig 39 Fig 40 .. Fig 41 Plate I. Acavthobothrium herdmani, n. sp. Entue cestode. x 4. Head of same, x 10. Cirrhus of same, x about 40. riatijbothrium spinulifera, n. s]}. Entire cestode. x 11. Head of same, x 50. Portion of neck of same, x 90. Bothridial hooks of same. X about 100. Anthobothriuin floraformis, n. sp. Entire cestode. x 20. Terminal proglottid of same, x 40. Head of same, x 40. Oragmatobolhrium tetraglobum, n. sp. Entire cestode. X about 30. A single bothridium of same from above, x about 9. Rhinebothrium shipleyi, n. sp. Entire cestode. X 4i. Head of same, x 10. One bothridium of same, x 16. Plate II. >Spongiobothriumlintoni,u. s]^. Entire cestode. x 8. Anthobothrium ceylonicum, n. sp. Entire cestode. x 12. Syndesmobolhrium filicolle. Cyst, x IJ. Larva of same. X 24. Telrarhynclms gangeticus. Larva. X 8. Cysts containing Otobothrmm insigne. X 2. A second, with transparent cyst containing same. X 2. Larva of same. X 15. Otobothrimn linstowi, n. sp. Enthe cestode. X 10. Head of same. X 16. Part of proboscis of same. Highly magnified. Phy iichobothrium, s]^.l. Larva. X 16. Cyst containmg larva of same. X 2|. A second larva of same. X 14. A hoolc from the proboscis of same. Highly magnified. Rhynchobothrium, sp. II. Cyst, x 4. Larva of same from cyst. X 13. Rhynchobothrium, sp. III. Cyst. X 2i. Larva of same from cj'st. X 25. Plate III. Rhynchoboihrimn,'s^. A.. Larva from cj^st. X 18. Rhynchobothrium, s^.B. Larva from cyst. X 20. Rhynchobothrium, sp. C. Larva from cyst. X about 25. Rhynchobothrium rossii, n. sp. Entire cestode. X 6. Head and neck of same. X 15. Termination of the proboscis of same, x 100. A hook from the proboscis of same. Highly magnified. Paratcenia elongatus, n. sp. Entire cestode. X 10. Tremalode . sp. X 2 CEYLON MARINE BIOLOGICAL REPORTS- PLATE I. GM.Hf.u-.v.del. l-;V/,luiDH.G..' CEYLON MARINE BIOLOGICAL REPORTS. PLATE II. G.M.Henr-y, d';l. iiV-'iiaon. Cambridge. CEYLON MARINE BIOLOGICAL REPORTS. PLATE 111. G.M Henry.del. £V/ilson. Cambridge. PRINTED AT THE GOVBBNMENT PRINTING OFFICE, COLOMBO, CEYLON.