must be remembered, are constantly floating through the water, ready to fasten on any vulnerable fish. The Tweed, then, may be taken as the type of salmon rivers in Britain, which have not their source in large lakes, as the Nith, Solway, Severn, &c. But rivers such as the Tay, flowing out of a loch, where one would expect nature had laid up an ample compensation for the modern loss of water in the river lower down, caused by excessive drainage, have also been found to be infected. In such cases I suspect the lake water cannot be sufficient in quantity or quality to effect the above object. At the same time it must be borne in mind that there is no evidence as yet of the discase in British waters draining a less cultivated area as Loch Lomond and its tributaries, the river Awe, and the rivers of the North of Scotland. On the other hand, North America and New Zealand furnish examples of fungus on salmon or trout living in waters where no appreciable alteration in chemical constitution can as yet have resulted from agricultural operations. The above ideas, stated generally, explain what I call the predisposing or primary causes of the outbreak of the salmon disease. But before discussing these further under my last division, the remedy, I may observe that I cannot entirely agree with the opinion expressed by Dr. Cooke and other scientific men, viz. that river pollutions, arising from town and factory drainage, have nothing to do with it. I am well aware that the fearful condition of the Tyne, below Newcastle-on-Tyne, has not as yet resulted in salmon forsaking that river, up which they still force their way on the top of a flood. It is likewise true that a score or two of this noble fish still run the gauntlet of the abominations of the Clyde at Glasgow, under favourable autumnal spates, and push up to their ancestral haunts below the Falls of Clyde. But I contend that not only is it but a question of time when the salmon will desert such rivers; I also believe that all excess of nitrogen contained in sewage will have the same bad effects on the fish as the manures I have already mentioned employed in agriculture. By excess of nitrogen, I mean the ratio of nitrogen to oxygen being too high for the health of the fish. 3. The proposed remedy.-Here it becomes necessary to refer to the natural history of the salmon, so far as now known, as being inseparable from a consideration of the three causes of the disease. The recruiting and feeding ground of the salmon is in salt, not fresh water. I speak, of course, of Salma salar. As a rule, with few exceptions, it does not feed during its ascent of fresh water rivers. One proof of this is in the fact that no food has as yet been found in the stomachs of salmon which had been any short time in a river. The salmon leaves the sea regularly and cleaves its way up a river in search of a nest or a place where it may, so to speak, form a seed-bed for its ova, and that as near the river's source as possible. This, its principal instinct, it follows to the neglect of all other considerations, food included. But when spawning is accomplished, then it seeks for nourish ment, and as it gradually drops down seaward again helps itself largely (as a kelt) to the young of the Salmonida-in the absence of more congenial food. The abstinence from its natural food while pushing upwards in a river to spawn must lower the fish's vital powers greatly. Then it is to be borne in mind that the salmon is in finest condition and greatest vigour when it first leaves the sea-fat, plump, and gleaming with its coat of burnished silver. this? It is simply because the sea covers its natural feeding grounds, where it can fatten on numberless crustaceans, molluscs, and small fish, which appear to suit its constitution admirably. Besides proper food, it gets more oxygen into its system in the sea. This is a matter requiring more investigation than has yet been devoted to it. Certain gases, it appears, are found secreted in the air bladder of all fishes furnished with that organ. Dr. Günther says:-" The gas contained in the air-bladder is secreted from its inner surface. In most fresh water fishes it consists of nitrogen, with a very small quantity of oxygen, and a trace of carbonic acid in sea fishes, especially those living at some depth, oxygen predominates, as much as 87 per cent, having been found. Davy found in the air-bladder of a fresh-run salmon a trace of carbonic acid, and 10 per cent. of oxygen, the remainder of the gas being nitrogen." We know also in fish culture that well ærated, or oxygenated, water is a necessity to the life of the young of Salmonidæ. Seeing then that the salmon is in its finest condition when in the sea, that is when its air bladder has most oxygen in it, and in its lowest condition when in the river after spawning, that is when we may believe least oxygen is in its airbladder, I think it a fair inference that these states of the airbladder may be taken as indices of the health of this fish. A gaseous analysis of the waters of affected and clean rivers, and of the contents of the air-bladder of salmon taken in these waters, would at this point be of great value. The only analysis in my possession is one made by the late Dr. Penny many years ago (1852), and I give it for what it may be worth now:— Parts. = 100 100 100 Carb. Acid. Oxygen. Nitrogen. ... Now, it is a curious coincidence at least, and favourable to my theory, that the Tay salmon are diseased, while those of Loch Lomond and Loch Ness are not. For the Tay water not only contains the smallest amount of oxygen of the three waters examined, but also the ratio of nitrogen to oxygen in it is highest. In other words, the waters of Loch Lomond and Loch Ness have not yet deteriorated so far as to encourage the outbreak of the fungoid disease. And in these lochs it appears there is more oxygen than in the water of the Tay, the absence of the necessary proportion of which I consider the principal cause of disease. This loss of oxygen, as before stated, is consequent on the progress of agriculture, which has reduced the average flow of salmon rivers, and at the same time increased the quantity of nitrogen supplied to them. To follow up the effect of these we must assume (what I think may be conceded) that the same run of salmon numerically takes place now as occurred sixty years ago. Given then a pool in Tweed, say "Gleddies Weel," which in 1822 carried a third more water than in 1882, and water with a larger proportion of oxygen in it, with 200 salmon in full vigor of life. How is it possible for the same number of fish at present to maintain health with a third less water, and vitiated at the same time by an overdose of nitrogen, delayed also, it may be, two months beyond their natural time of reaching that pool? But there are many rivers of North Western America still unaffected by agriculture, and waters in New Zealand as pure, where this fungoid or a similar disease is known. This may fairly be urged against my theory, but it is not therefore unanswerable. In the long American rivers, as the Fraser, the habit of the salmon, S. quinnat, or S. chonicha, is the direct cause of the disease. For even after this fish has travelled up hundreds of miles from the sea and spawned, it still presses upwards, losing condition and strength daily, and gets scarred and bruised by rocks till its vitality is reduced beyond the point where it can throw off the attacks of fungus, and to which it eventually succumbs, and dies covered with a mass of offensive sores. Again, in Queenstown Bay, Lake Wakatipu, New Zealand, where the water is pure and abundant, and the trout remarkably fat, this fungoid disease is widespread. In this case there is a total absence of salt in the water, and all fish above a certain size are unable to ascend their native stream, the Town Creek, owing to its smallness, to spawn. These two reasons appear to me enough to make the trout subject to the disease, and, as a matter of fact, they die from it, although as yet not in great numbers. In a word, then, the blood of the salmon when deprived of its proper quantity of oxygen deteriorates, and thus so weakens the fish as to leave it with no vigour of life or strength sufficient to throw off the seeds of the fungoid disease. Finally, contrasting, then, the above facts-lowness of rivers, want of oxygen, excess of nitrogen, prolonged residence of salmon in the riveis with fungoid disease prevalent, as at present; and on the other hand, plenty of water, free passage of fish, fish abundant and healthy, as obtained sixty years ago-and the conclusion is plain that the disease in Tweed, &c., is due not to a single specific cause, but to those connected with the altered state of the rivers, and that the remedy must lie in restoring these rivers to their previous condition so far as practicable. This restoration can only be effected by the general concurrence and united action of all the higher and lower proprietors, assisted in the first outlay by a Government subsidy. In other words, compensation reservoirs must be constructed on all the tributaries of salmon rivers, to impound the excess of flood waters, and from which reservoirs it may be delivered during the dry months to assist the salmon in its ascent and descent. This is the first essential to success in eradicating fungus. Next, rock salt should be used in wells below the sluices of the reservoir, to yield its well-known health-giving properties to the water as it passes over it. All rivers, caulds, and dams, should be furnished with the most approved fish-ladders, so as to afford a clear run to the salmon in low states of the rivers, and stake nets, with other nets, must be removed one mile from the mouths of the rivers. If these, or like remedies, be not adopted, I see no other way of assisting nature to cure the salmon of British rivers of this fatal disease. Roslyn, December, 1882. NEW ZEALAND SHELLS OF THE "CHALLENGER" EXPEDITION. BY THE REV. R. BOOG WATSON, F.L.S., ETC. (Continued from Page 321.) PLEUROTOMA (SURCULA) ISCHNA, Watson, Zool. xv., p. 403. Proc. Linn. Soc., St. 169. July 10, 1874. Lat 37° 34′ S., lon. 179° 22′ E., N.E. from New Zealand. 700 fms., grey ooze. Bottom temperature, 40°. Shell.-High, narrow, conical, blunt, with a contracted base and longish snout, little sculpture, yellowish grey, porcellaneous. Sculpture.-Longitudinals-these are only strongish regular lines of growth, which rise into small tubercles, especially on the upper whorls; between the stronger lines the surface of the shell is delicately fretted with other very minute sharp lines. Spirals.The whorls are faintly keeled above the middle by a spiral thread, which is a little stronger and more prominent than any of the others. Close above the suture is another, almost as strong, and which also slightly carinates the whorls; half-way between these is a finer thread, which tends to split into two very fine threads; at the suture, but visible beyond the mouth, is another thread, which here defines the base. The longitudinals rise into very small tubercles as they cross the spirals; but this feature is much the strongest on the upper whorls, which are reticulated; on the last whorl it is feeble. Between the keel and the suture lie three very fine, equally-parted threads. On the base and snout are. about twelve pretty equal fine threads. Colour a faintly yellowish-gray. Epidermis extremely thin, smooth. Spire conical, with an almost unbroken profile, the whole being scarcely convex. Apex.-There are barely two embryonic whorls, smooth, globose, not flattened down at the tip, which, however, is slightly immersed. Whorls, 7 in all, feebly keeled with a just perceptibly concave line from the suture to the keel, and from the keel to the suture below. Just above the suture there is a slight con traction, which forms a faint superior margination. The last whorl is very slightly swollen; the base is rather rapidly contracted, and is drawn out into a rather long, straight, but not narrow snout. Suture distinct, impressed. Mouth almost clubshaped, being pointedly oval above, with a longish rather sinuous canal below. Outer lip forms a regular curve, till at the canal it becomes flattened and oblique; from the body it retreats at once to form the rather deep, rounded, open-mouthed sinus, from which it advances on a very straight line to the edge of the canal in front, where it bends slowly and slightly backwards; it is throughout open, but not patulous except at the point of the canal. Inner lip spreads as a narrow porcellaneous glaze on the body and pillar; it is slightly hollowed out on the body, is straight on the pillar, toward the front of which it is cut off with a narrow, rounded, and very slightly oblique edge. H. 0.34; B. 0.09. Penultimate whorl, height 0.05. Mouth, height 0.14, breadth 0.05. This species is very like P. emendata, Monterosato (= P. Renieri, Phil., but not really that of Scacchi); but is much narrower, has much finer and differently arranged spirals, which are minutely tubercled, the curved cusps of the old sinuses are much feebler, and the longitudinals between the threads are far less distinct. The apical whorls are much less depressed. PLEUROTOMA (GENOTIA) ENGONIA, Watson, l.c., p. 405. (?) St. 169. July 10, 1874. Lat. 37° 34' S.; long. 179° 22′ E N.E. from New Zealand. 700 fms., grey ooze. Bottom temperature 40°. St. 232. May 12, 1875. Lat. 35° 11' N.; long. 139° 28′ E. Off Inosima, Japan. 345 fms., sandy mud. Bottom temperature 41.1°. Shell.-Fusiform, biconical, with an expressed rounded keel angulating the whorls, and broad, prominent, lop-sided snout. Sculpture.-Longitudinals-there are no ribs. The lines of growth are strong, hair-like, unequal and close-set; on the keel, which marks the line of the old sinuses they are exceptionally strong, prominent, regular, and a little remote, as they also are at the top of the whorls in the suture; still they are throughout rounded, not sharp. Spirals.-The whorls are angulated about the middle, and project in a rather narrow, prominent, rounded keel, which is almost crenulated by the lines of growth. The whole surface is also covered by small, broadish, rounded, closeset spiral threads, which are somewhat granularly tubercled below the keel. On the left side of the point of the snout they tend to become obsolete, as they also do on the earlier regular whorls. Colour, porcellaneous white. Epidermis only one minute fragment remains, which seems thin, yellowish, and membranaceous. Spire, high, sub-scalar, typically conical, the profile lines being very little interrupted by the carinal projection. Apex blunt, rounded, consisting of two smooth globular whorls. |