[&&] FISHEEIES OF THE UNITED STATES. 567 



iron frame of one-half-inch round iron, 3 feet long and 8 inches wide, 

 is swung loosely, by means of handles about 12 inches long, from a 

 piece of iron gas-pipe, which is of the proper diameter tifc fit into the 

 ends of the pipe forming the beam of the trawl, into which it reaches a 

 distance of 1 foot or more. A large screw on the end of the beam holds 

 it firmly in place. The frame is furnished with a coarse net, measur- 

 ing from 3 to 4 feet in length and having about 3 meshes to the linear 

 inch. The ordinary towing net, as described above, is now fastened into 

 the coarse net by tying the ring to it, far enough from the mouth, so that 

 the lower end of the fine net reaches nearly to the end of the larger 

 one. Two arrangements of this kind are always used, one at each end 

 of the beam. They are called the trawl wings, and the entire appara- 

 tus thus made up is termed the butterfly trawl. 



Sigshee's Gravitating Trap for collecting animal forms from intermediate 

 ocean depths. 



Commander Charles D. Sigsbee, United States Navy. 



The old practice of dragging for animal forms at intermediate depths 

 by means of a tow-net, which during the several operations of lowering, 

 dragging, and hauling back remained open, not being regarded as afford- 

 ing sufficient evidence of the habitat of such specimens as were obtained, 

 this apparatus was invented by Commander Sigsbee, at the request of 

 Prof. Alexander Agassiz, who afterwards used it with success. (See 

 Bulletin of the Museum of Comparative Zoology at Harvard College, 

 vol. vi, ISos. 8 and 9, September, 1880.) The following explanation is 

 drawn chiefly from No. 9 of the Bulletin, which was written by Com- 

 mander Sigsbee. 



"Our plan is to trap the specimens by giving to a cylinder, covered 

 with gauze at the upper end and having a flap valve at the lower end, 

 a rapid vertical descent between any two depths, as may be desired; the 

 valve during such descent to keep open, but to remain closed during 

 the processes of lowering and hauling back with the rope. An idea of 

 What it is intended to effect may be stated briefly thus : Specimens are 

 to be obtained between the intermediate depths a and b, the former 

 being the uppermost. With the apparatus in position, there is at a the 

 cylinder suspended from a friction clamp in such a way that the weight 

 of the cylinder and its frame keeps the valve closed; at b there is a fric- 

 tion buffer. Everything being ready, a small weight or messenger is 

 sent down, which on striking the clamp disengages the latter and also 

 th&cylinder, when messenger, clamp, and cylinder descend by their own 

 weight to &, with the valve open during the passage. When the cylinder, 

 frame strikes the buffer at b, the valve is thereupon closed, and it is kept 

 •closed thereafter by the weight of the messenger, clamp, and cylinder. 

 The friction buffer, which is 4 inches long, may be regulated on board 

 to give as many feet of cushioning as desired." 



The following is a detailed description : A copper cylinder, riveted 



