Engle ; s data also clearly express, within the temperature range of his experiments, 

 the wide range of variation of death times for different drills even at a given salinity. 

 For example, in a salinity of 5 o/oo the first drill died in approximately 4 days, 50% 

 of the drills died in 9 days, and 100% in 11 days; in 12 o/oo the first drill died in 5 

 days, 50% in 16 days, 100% in 30 days; in 14 o/oo the firet drill died in 5 days, 50% 

 in 15 days, and 100% in 49 days . At a salinity of 14 o/oo the relation between 

 temperature and salinity death times, so nicely established at lower temperatures, 

 disappeared: at a mean temperature of 17.5°C, 100% mortality occurred in 18 days, 

 at 18 .2 and 20 . 1 in 25 days, "and at 20 .5° C in 49 days . Engle concludes that within 

 the temperature range of 15 ,4 to 23 0°C the minimum salinity tolerance level of 

 these drills lies somewhere between 14 and 16 o/oo, a range intermediate between 

 those given by Federighi for Hampton Roads and Beaufort drills, 



Although the designs of the various experiments on the salinity death times 

 of the oyster drill differ considerably, it is demonstrated in some of the experi- 

 ments and may be inferred from others that at temperatures close to those of 

 summer conditions drills do not generally survive below the following approximate 

 salinities: 



17 o/oo, Beaufort, North Carolina (Federighi, 1931c); 

 12 o/oo, Hampton Roads, Virginia (Federighi, 1931c); 

 16 o/oo, Long Island Sound, Connecticut (Engle, 1953); 

 12-15 o/oo, Lower Delaware Bay, New Jersey (Sizer, 1936; 

 Galtsoff etah, 1937; Stauber, 1943). 



The researches on salinity show conclusively that the variables of tempera- 

 ture and time exert a significant influence on rate of survival: at optimum summer 

 temperatures drill mortality rates increase rapidly as salinities fall, but this rate 

 is markedly reduced as temperatures drop, so that at low winter temperatures 

 Uro salpinx can withstand unusually low salinities for protracted periods . It is 

 further indicated that early conditioning of the drill also influences survival 

 (Federighi, 1931c; Stauber, pers. com.). 



Movement 



The rate of movement exhibited by Urosalpinx in the narrow salinity zones 

 at either extreme of its normal salinity range has not been satisfactorily explored . 

 Sizer (1936) in laboratory experiments at 24°C made the unrealistic observation that 

 drills were inactive at salinities below 20 o/oo and above 30 o/oo s and that they crept 

 most rapidly at about 25 o/oo or above Stauber (1943) believes that Sizer did not 

 allow sufficient time for his drills to adjust to the experimental salinities He 

 questions Sizer' s figures on the basis that he collected drills in drill traps in some 



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