[29] INSTRUCTIONS FOR COLLECTING MOLLUSKS DALL. 



The ring at the front end of each arm should be bent vertically so that 

 when the two arms are brought together in front of the dredge the two 

 rings will be exactly oiDposite, and lie flat against each other. For the 

 galvanized iron a strip about 2 inches in width is sufficient. This also 

 should have the holes for the lacing punched into it and filed smooth 

 before it is riveted to the frame, as it is much more difficult to do it 

 afterward. 



Suitable nets made expressly for dredges can be obtained from the 

 Gloucester Net and Twine Company, Boston, Mass., or from any other 

 manufacturers of nets. The net when dry is usually about 2 feet long; 

 the meshes of the front part of it about half an inch in diameter. The 

 bottom of the bag has smaller meshes, and is usually made double, or 

 with double twines. Various sizes can be had to fit the dredge by 

 mentioning the size of the frame in the order. 



In deep-sea dredges, used by steam, it has sometimes been found that 

 when the dredge first reached the bottom it cut so deej) into the soft 

 mud as to fill itself full at once, thereby preventing anything else from 

 getting in. This difficulty was remedied by fitting a pair of wooden 

 runners to the sides of the dredge, which would not allow the edge of 

 the dredge to cut into the bottom until it had assumed a horizontal 

 position. In ordinary dredging no precaution of this sort is necessary, 

 since the dredger after a little experience will learn to regulate the 

 length of the line and the position of the dredge for himself. 



In attaching the dredge to the line it is usual to have a short piece 

 of rope permanently attached to the frame. This rope may be 10 or 15 

 feet long. The front end is spliced to form a loop about 6 inches long. 

 Into this loop the long dredge-line can be knotted when it is needed for 

 use. The other end of the short rope is passed through one of the rings at 

 the front end of one of the arms, then along the arm to one of the 

 rings by which the arm is attached to the frame. Here the line is sol- 

 idly fastened. When in use, the front ring of the other arm is attached 

 to the opposite ring, through which the short rope passes, by means of 

 a piece of ordinary twine, and it will be observed that the rope in no 

 case should pass through both the front rings of the two arms. This is 

 because it frequently happens that a dredge on the bottom may catch 

 upon a bowlder or on other obstructions too heavy to be moved. If the 

 rope passed through both arms of the dredge, the latter could not be 

 raised, and therefore, with the line attached to it, would be lost. But 

 when one of the rings only is tied with twine, by pulling hard upon the 

 line the twine may be broken, and the two arms of the dredge will pull 

 out straight and the latter may be recovered without damage. 



In order to xjrevent the dredge from being raised above the surface of 

 the bottom at its front edge by the inclination of the line to which it is 

 attached, it is usual to attach a weight to the line some distance in 

 front of the dredge, which makes the part of the rope behind that weight 

 assume a more horizontal position . A convenient weight for this i3urpose 



