424 Birge — Vertical Distribution of Pelagic Crustacea. 



the weights for moving the cover, and the attachment for the 

 net. 



The frame is 44 cm. long by 23 cm. wide on the outside, 

 42 cm. by 20 cm. inside. It is made of brass tubing 1 inch 

 square and 1-32 of an inch thick, split longitudinally so as to 

 leave one flange — the top one — f- of an inch wide, and the 

 other ■§- of an inch wide. (A, PI. VIII, fig. 1.) The pieces are firmly 

 soldered together so that the flanges project outward. At the 

 corners are fastened ears, pierced for the four cords by which 

 the frame is hung to the dredge line. A half-piece of tubing 

 similar to that of the frame is soldered across the frame near 

 the middle, so as to leave an opening at one end 20 cm. square. 

 Beneath this opening is fastened the net, and this end is called 

 the front of the frame. 



To the top flange on the sides of the frame and across the 

 front end is soldered a strip of sheet brass 1-32 of an inch 

 thick, and about \ of an inch wide. (J5) This is attached 

 close to the outside of the upper flange. Above it is fastened a 

 strip of thin spring brass — the guide ( C) — of the full width 

 of the top flange, leaving between it and the flange a deep 

 narrow cleft open toward the inside of the frame. In this 

 groove the cover slides. Jn the middle of each end of the frame 

 is attached a pulley {H), over which pass the cords for moving 

 the cover. Just above the front pulley is an eye of wire (G), 

 through which passes the cord to the cover. Its purpose will 

 be mentioned later. 



The cover is a flat piece of thin spring brass. The sides and 

 front edge are not modified at all. The rear edge is bent over, 

 so that when closed the cover fits closely over the flange of the 

 partition in the middle of the frame. Around the front and 

 sides of the cover is soldered a strip of thin sheet copper -fa 

 of an inch thick, and f of an inch wide. ( E) The inner edge 

 of this strip is folded on itself, and attached to the cover so 

 that the free edge is parallel with that of the cover, leaving be- 

 tween it and the cover a deep, narrow groove, in which fits 

 the guide of the frame. On the top of the cover are soldered 

 two eyes (J) for the attachment of the weight cords. In a 

 dredge which is to be worked from a large boat it is well to 



