2Y4 ON COLLECTING SHELLS. 



the plane of the dredge's mouth, so that when the dredge was 

 gently hauled along it took hold of the ground and secured 

 anything loose on the surface. I haA'^e seen Dr. Ball scatter 

 pence on the drawing-room floor and pick them up quite dexter- 

 ousl}^ with the dredge drawn along in the ordinarj^ dredging 

 position. 



" Latterly Ball's dredges of considerably larger size have been 

 used. Perhaps the most convenient form and size for dredging 

 from a row-boat or a yawl at depths under a hundred fathoms, 

 has a frame eighteen inches long, and its width is five inches. 

 The scrapers are three inches wide, and they are so set that the 

 distance between their scraping edges is seven inches and a half. 

 The ends of the frame connecting the scrapers are round bars 

 of iron five-eighths of an inch in diameter, and from these two 

 curved arms of round iron of the same thickness, dividing 

 beneath into two branches which are attached to the ends of the 

 cross-bars by eyes, allowing the arms to fold down over the 

 dredge-mouth, meet in two heavy eyes at a point eighteen inches 

 above the centre of the frame. The total weight of the dredge 

 frame and arms is twenty pounds. It ought to be of the best 

 Lowraoor or Swedish wrought-iron. I have seen a stout dredge 

 frame of Lowmoor iron twisted like a bit of wax in extricating it 

 from a jam between two stones, and, singularly enough, the 

 dredge which came up in that condition contained the unique 

 example of an echinoderm never found before or since. 



" The thick inner edges of the scrapers are perforated by round 

 holes at distances of about an inch, and through these strong 

 iron rings about an inch in diameter are passed, and two or three 

 like rings run on the short rods which form the ends of the 

 dredge frame. A light iron rod bent in the form of the dredge 

 opening usually runs through these rings, and to this rod and 

 to the rings the mouth of the dredge base,is securely attached 

 by a stout cord or strong copper wire. 



" In the dredge now before me, which has worked well and 

 seen good service, the bag is two feet in depth, and is of hand- 

 made net of very strong twine, the meshes half an inch to the 

 side. So open a network would let many of the smaller things 

 through, and to avoid this the bottom of the bag, to the height 

 of about nine inches, is lined with " bread bag," a light open 

 kind of canvas. 



" Many other materials have been used for dredge bags : one 

 which I have used frequently is made of sail-cloth, with a window 

 of strong brass-wire gauze let in on either side. Nothing, how- 

 ever, seems to me so good as strong cord netting. The water 

 passes easily through and carries with it a large part of the fine 

 mud, while enough mud is retained by the bread-bag lining in 

 the bottom to give a fair example of its cout^ents. It may be 



