BULLETIN OF THE UNITED STATES FISH COMMISSION. 25 



mud, which, indeed, is almost universally devoid of life of any kind.''* 

 This remark, which was meant to apply to small organisms found in 

 fresh water, applies with equal force to those found in brackish or sea 

 water, because the fresh- water and marine faunoe and Horse of micro- 

 scopic forms really blend together or overlap. It is therefore evident 

 that ooze or mud on the bottoms of oyster beds or ponds iu excess is 

 invariably to be regarded as injurious both to the oysters themselves 

 and to the minute organisms upon which they feed. 



To prevent iu a measure the accumulation of sediment on the bottom 

 of oyster ponds and coves the introduction of sand filters will be found 

 effective in proportion to the practical skill and knowledge brought to 

 bear in their construction and management. I do not mean to affirm 

 that the form of diaphragm here described will be found to be the most 

 suitable means of attaining our object after prolonged experience has 

 been had in the work. It may be found in using a single diaphragm, 

 through which the water may flow in either direction alternately, that 

 when the flow is reversed a certain amount of sediment will be washed 

 out of the sand filter, and that when this occurs during the inflow into 

 the pond a certain quantity of sediment would be carried in and de- 

 posited. If this should be found to be the case it would be an easy matter 

 to arrange two separate diaphragms in a trunk divided by a longitudi- 

 nal vertical partition alongside of each other. One of these might be 

 arranged, as shown in Fig. 1, to filter only the inflowing water and the 

 one alongside of it to filter the outflow. They could be made to operate 

 automatically if wooden valves were provided at the inlet and outlet of 

 either, so arranged as to close and open when the pressure of the tide 

 was least or greatest as the latter rose and fell, but such complications 

 in the construction of filters or diaphragms would only make them more 

 difficult to operate and less suited to be left to the management of the 

 ordinary laborer. If it is possible, therefore, to keep out the sediment 

 with the simple form here described, it would be much better to stick to 

 that without additional complications. The confinement of the brood 

 or fry either thrown off from old oysters living in the pond or of such 

 as has been artificially introduced into the inclosure, as was done at 

 Stockton, would be well enough accomplished, in all probability, by a 

 simple diaphragm such as that here described. 



The freedom of the flow through the diaphragm will depend mainly 

 upon the area of the latter and the fineness of the sand composing the 

 filtering stratum. And it would therefore be possible to construct a fil- 

 ter of a capacity great enough to filter enormous volumes of water, or 

 enough for the very largest operations, by simply increasing the area 

 of the filtering surface. The obstruction or clogging of the filter by de- 

 posits of fine and coarse materials on the top of the stratum of sand 

 might be obviated to a large extent by the use of wire screens placed 



* Fresh-water Eliizopoda of North America. By Joseph Leidy, M. D. Eep. U. S. 

 Geol. Surv. Terr., vol. xii, 1879, pp. 8 and 9. 



