Collection and Preparation 21 



sieve and wash thoroughly, examine what remains for small mollusks; 

 many of these and other small sand-dwellers will be seen. Repeat 

 this digging and sifting at successive depths in the same spot in 

 order to learn what species live near the surface and which ones 

 burrow more deeply. Continue this process at increasing distances out 

 from shore and in bottoms of different character. Slightly different 

 conditions within a circumscribed locality will afford congenial sta- 

 tions to various species of mollusks. In protected inside waters with 

 varying depths and character of bottom, a great number of species 

 find favorable circumstances and attain perfect development. 



The frame of a crabnet rather tightly covered with good qual- 

 ity fine-meshed net or coarse scrim is useful for collecting those 

 species which live among grass or seaweed. The net should be used 

 with a scooping movement, just escaping bottom. 



Baited traps may be set and left for 24 hours, at least over- 

 night, since many mollusks are nocturnal feeders. When set in 

 water deep enough to cover the trap, the location should be marked 

 by a buoy. Shrimp, crab, and fish are best for bait, though dead mol- 

 lusks and bits of meat will attract carrion feeders. Sand fleas (Hip- 

 pidae) have proven exceedingly attractive bait to Oliva. 



Dredging is the only method of taking living shells of other 

 than shallow water species. By this means material is secured which 

 is otherwise inaccessible or at best represented by occasional beach- 

 worn specimens. In the type of dredge most satisfactory for general 

 work, the cutting blades should be at an angle of about 165 degrees 

 with the bottom of the dredge and the dimension between top and 

 bottom not less than 10 inches. Scallop dredges and tangles have 

 also been used successfully, and a short section of cast iron pipe 

 with a perforated bottom and suitable means of attachment for 

 chains and tow rope is advantageous for learning characters of 

 bottom. Dredges are drawn behind a motor boat with a stout rope 

 two or three times as long as the depth of water — the deeper the 

 water the greater the proportionate length of the tow rope. Five or 

 six feet of galvanized iron chain is attached to each arm of the dredge 

 and joined with a swivel to the towing rope. When dredging is under- 

 taken in depths of water exceeding four or five fathoms a weight 

 should be attached to the tow rope about ten feet ahead of the 



