BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 17 



dredge is practically certain to drag in such a way that one or the other of these edges is 

 lowermost. 



A modification of this type of dredge which was freely used during the present work 

 was the " rake dredge," which differs from the ordinary pattern in possessing heavy teeth 

 along the cutting edge. The frame, in both types, is fitted with two heavy movable 

 iron arms, to which the dredge line is attached. Commonly a comparatively light rope 

 was fastened to one of these handles, so that in case an obstruction was encountered 

 this line might part and allow the dredge frame to free itself without escaping altogether. 

 The dredge net was protected from tearing by a sheathing of heavy canvas, which was 

 attached to the frame outside of the net and formed a bag, open at the lower end. The 

 netting commonly employed in these dredges had a 4^-inch or a i-inch mesh" in the 

 upper portion, while the lower end was quite closely woven. Such meshes were likely 

 to retain not only the stones, shells, and the great majority of living organisms, but 

 even considerable quantities of the bottom material. Fine loose sand, however, and in 

 less degree mud, were likely to be washed out almost completely during the reeling in 

 of the dredge line. Where such bottoms were encountered, the canvas sheathing of the 

 dredge was frequently tied up at the lower end, or sometimes a simple canvas bag alone 

 (mud bag) was attached to the frame. During the last season of the regular dredging 

 work (1905) the mud bag was nearly always employed in connection with the beam 

 trawl. It is obvious that a much fairer bottom sample could be collected in this way. 

 The dimensions of the frame in the type most commonly used during the Fish Hawk 

 dredging were 12 by 22 inches. A smaller size (8 by 16 inches) was, however, some- 

 times used in the Pkalarope and Blue Wing work. 



(3) The third type of dredge employed was the "oyster dredge." This was inter- 

 mediate in size between the beam trawl and the scrape dredge and was very heavily 

 constructed, being well adapted to use upon rocky bottoms. The scraping edge at the 

 mouth of this implement was armed with powerful spikes or teeth, designed to dig deeply 

 into the sand or gravel. The bag of the dredge was made up of iron rings, linked 

 together after the fashion of chain annor. In order to retain the smaller organisms, 

 this chainwork bottom was commonly lined with fine netting. The oyster dredge was 

 employed on bottoms too stony for the other appliances, or where it was desired to 

 penetrate more deeply beneath the surface. 



The Fish Hawk is a steam vessel having a length of 146 feet at the water line, or 

 of 156 feet over all, a beam of 27 feet, and a draft of about 7 feet. She carries adequate 

 machinery for the reeling in of heavy dredges, and despite her Hmited speed and unsea- 

 worthy construction is an extremely serviceable vessel for scientific operations in quiet 

 waters. A full description of the Fish Hawk has already been given by Tanner (1884), 

 and therefore need not be repeated here. 



The material taken by the Fish Hawk dredges was commonly emptied into a series 

 of trays, constituting the table sieve of Verrill and Chester (Verrill, 1883), having graded 

 meshes, the coarser ones naturally being uppermost. After a superficial examination 

 and preliminary search for specimens a stream of salt water was played upon the mate- 

 rial, and the sand, mud, and small unattached organisms were thus washed into the 



o These measurements refer to the "stretched" mesh. Such meshes would be i inch or -i inch square when open. 

 16269° — Bull. 31, pt I — 13 2 



