BULLETIN OF THE UNITED STATES FISH COMMISSION. 37 



than deep. The soil removed should be plowed up and shoveled to the 

 lower or pond side. When the question of getting rid of the floods is 

 disposed of, the dam may be built. 



VVasteways. — Many persons will not attempt to turn the floods 

 around the dams by makiug canals, and therefore I would recommend 

 that the wasteways to their dams should be cut around the end through 

 the natural soil of the hill-side. This form of wasteway is merely a 

 wide ditch, cut without fall, and extending far enough below the lower 

 side of the dam to prevent the waste water from cutting that side of 

 the dam away. Two or more rows of piling to arrest the cutting out 

 may be required to be driven across this outlet, the upper ends being 

 even with the bottom of the ditch. A row of narrow strips of boards 

 may be driven in the mud close together in the pond above the mouth 

 of this ditch to serve as a screen. If this screen or fence is located in 

 4 or 5 feet of water, and the two ends drawn in to the shore, it will be 

 twice as valuable as if built immediately at the ditch mouth, for more 

 surface would be exposed. The strips or stakes should be driven a 

 foot into the soil below, and their upper ends on a level with the top of 

 the dam. No dam, however small, should be built without a box in the 

 bottom, provided with a gate, for drawing the water. Such a box 

 should be made 6 or 10 inches square, of 2-inch plank, and reach en- 

 tirely through the dam, and much pains must be observed to make 

 it long enough. It should be well nailed together and be placed into 

 the bottom of the dam at the lowest point. It should be placed upon 

 one or more pieces of scantling laid in the soil at the base of the dam, 

 and be nailed to these to prevent the water flowing under. The earth 

 can be packed above and on the sides, the timbers being necessary only 

 underneath. A gate should be put into the upper or pond end. 



No dam should be made until a ditch has been cut along the line 

 which it will occupy, and the light soil thrown out. Fresh earth put 

 back into the ditch, well rammed, will prevent blowing out if the ditch 

 is dug 2 or more feet. Ponds for raising the carp should be shallow, 

 not more than from 2 to 4 feet deep, except at the dam, where there 

 may be a depth of 5 or 6 feet. 



13.— ON A SKIN PARASITE OF THE CUJVNER (CTENOLABKU8 AD- 



SPEBSIJS). 



By JOHN A. RYDER. 



Shortly after my return frpm Wood's Holl, Mass., an interesting spec- 

 imen of the common Gunner, Chogset, or Blue Perch, was sent on Irom 

 that place by Vinal N. Edwards, to Washington, on account of the pecu- 

 liar spotted and rough appearance presented by the skin. At first one 

 might have supposed that the i)eculiar whitish spots, with a dark halo 

 of pigment around each of them, were j)oints where some minute fungus 



