ON COLLECTING SHELLS. 273 



the sea, until it was employed by 0. F. Miiller in the researches 

 which afforded material for the publication in 1799, of his 

 admirable ' Descriptions and History of the Rarer and Less- 

 known Animals of Denmark and Norway.' In the preface of 

 the first volume Miiller gives a quaint account of his machinery 

 and mode of working which it is pleasant to read. 



" The instrument usually emploj^ed for dredging oysters and 

 clams is a light frame of iron about five feet long, by a foot or 

 so in width at the mouth, with a scraper like a narrow hoe on 

 one side, and a suspending apparatus of thin iron bars which 

 meet in an iron ring for the attachment of the dredge rope on 

 the other. From the frame is suspended a bag about two feet 

 in depth, iron chain netting, or of wide-meshed hempen cord 

 netting, or of a mixture of both. 



" Naturalist dredgers first used the oyster dredge, and all the 

 diff'erent dredges now in use are modifications of it in one 

 direction or another ; for in its simplicity it is not suitable for 

 scientific purposes. The oyster dredge has a scraper oul}^ on 

 one side. In the skilled hands of the fishermen this is no dis- 

 advantage, for it is always sent down in such a wa}" that it falls 

 face foremost ; but philosophers using it in deep water very 

 generally found that whether from clumsiness or from want of 

 sufficient practice, they had got the dredge down on its back 

 and of course it came up empty. Again oyster dredgers are only 

 allowed to take o^^sters of a certain size, and the meshing of the 

 commercial dredge is so contrived as to allow all bodies under 

 a certain considerable size to pass through. This defeats the 

 object of the naturalist, for some of the prizes to which he 

 attaches the highest value are mites of things scarcely visible 

 to the unaided eye. 



" The remed^r for these defects is to have a scraper on each 

 side, with the arms attached in such a way that one or the other 

 of the scrapers must reach the ground in whatever position the 

 dredge may fall ; and to have the bag deeper in proportion to 

 the size of the frame, and of a material which is only sufficiently 

 open to allow the water to pass freely through, with the openings 

 so distributed as to leave a part of the bag close enough to bring 

 up the finest mud. 



" The late Dr. Robert Ball, of Dublin, devised the modification 

 which has since been used almost universally by naturalists 

 under the name of " Ball's Dredge." The dredges on this 

 pattern used in Great Britain for ten years after their first intro- 

 duction about the year 1838, were usually small and rather 

 heavy — not more than from twelve to fifteen inches in length 

 by four to five and a half inches in width at the mouth. There 

 were two scrapers the length of the dredge-frame and an inch 

 and. a half or two inches wide, set at about an angle of 110° to 



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