re devices for collecting burrowing creatures
without filling the dredge with the soil in which they live. Holt
used, at Plymouth, a dredge whose side bars and lower lip were of
iron, the latter armed with forward and downward pointing teeth which
stirred up the sand and its denizens in front of the dredge mouth. The
upper lip of the dredge was replaced by a bar of wood. The bag was of
cheese-cloth or light open canvas, and the whole was of light
construction. The apparatus was very useful in capturing small
burrowing crustacea. The Chester rake dredge is a Blake dredge in
front of which is secured a heavy iron rectangle with teeth placed
almost at right angles to its long sides and in the plane of the
rectangle. Each of these instruments has a width along the scraping
edge of about 3 ft.

_Triangular and Conical Dredges._--Two other dredges are worthy of
mention. The triangular dredge, much resembling Muller's but with a
triangular mouth, and hung by chains from its angles, is an old
fashion now not in general use. It is, however, very useful for rocky
ground. At the Plymouth marine laboratory was also devised the conical
dredge (1901), the circular form being the suggestion of Garstang.
This dredge (fig. 16) was intended for digging deeply. It is of
wrought iron, and of the following dimensions: diameter of mouth 16
in., length 33 in., depth of ring at mouth 9 in. Its weight is 67
lb. As at first used the spaces between the bars are closed by wire
netting; if used for collecting bottom samples it is furnished with a
lining of strong sail-cloth.

[Illustration: FIG. 16.--Conical Dredge being hoisted in.]

Its weight and the small length of edge in contact with the ground
cause this dredge to dig well, and enable the user to obtain many
objects which though quite common are of rare occurrence in an
ordinary dredge. Thus on the Brown Ridges, a fishing-ground west of
Holland, although _Donax vittalus_ is known from examination of fish
stomachs to be abundant, it is rarely taken except in the conical
dredge: the same is true of _Echinocyamus pusillus_, which is in many
parts of the North Sea abundant in bottom samples and in no ordinary
dredgings. With the sail-cloth lining the conical dredge fills in
about 10 minutes on most ground, and no material washing out of fine
sediment occurs on hauling. In shallow seas such as the North Sea
commercial be