210 SHELL DREDGING. 
form the scraping edge, as represented in the cut at the close 
of this article. The other edge must be drilled with small 
holes an inch apart, to which a stout cloth bag is to be 
sewed. It is well to have the sides of the bag made of 
netting so that the water may drain from it quickly. The 
iron shanks are to be fastened to the dredge, as shown in 
the figure. A dredge of this shape, however it falls, when 
drawn slowly along, is sure to scrape up the mud. It 
is well to have for a rope a good strong one of manila- 
hemp, and this should be well secured to the dredge. It is 
necessary to have the length of the rope more than twice 
the depth you intend to dredge in; thus, if you were to 
dredge in ten fathoms, you should be provided with at least 
twenty-five fathoms of rope, as it is necessary to give the 
dredge sufficient "slack" in order that it may drag properly. 
Should the dredge meet with any obstacle, it can generally 
be liberated by retracing the track passed over, dragging 
the dredge in an opposite direction. It is well to add that 
a row-boat is best to dredge from, that is for light dredges, 
as you want to move very slowly through the water. A fine 
sieve is necessary to sift out the mud, a few pails in which to 
empty the contents of the dredge, and some large-mouthed 
vials in which to save the animals alive. — 
After a little experience in dredging you will notice that 
certain species live on certain "bottoms." Thus, if your 
dredge comes up filled with mud, you must sift the mu 
carefully, and from it you will find certain forms different 
from those you may dredge from a sandy bottom. It is well 
to examine your sieve often, that the smaller species may 
not be washed away. Sometimes the dredge will come UP 
filled with stones; do not throw these away in disgust, but 
examine each stone carefully, and clinging to them you will 
find several species of shells found in no other way. One 
species, called Cemoria Noachina (Pl. 4, figs. 2, 3), is like. 
| & very small limpet, with a little hole in its top from which 
. radiate little ribs, giving the shell a very elegant appearance 


